CVE-2026-49864

### Summary The wetty client decodes a base64 filename from the file-download escape sequence and interpolates it raw into a Toastify HTML string (`escapeMarkup: false`). Any output the victim renders - a `cat`'d file, a tailed log, an SSH MOTD, a `curl` response - that contains `\x1b[5i...:...\x1b[4i` runs script in the wetty origin and types attacker-chosen keystrokes into the victim's SSH session. ### Preconditions - Victim has wetty open with an active SSH session. - Attacker delivers the file-download escape sequence (`\x1b[5i<b64-name>:<b64-content>\x1b[4i`) into output the victim's terminal renders. - Default configuration; no non-default flags required. ### Details ```typescript // src/client/wetty.ts:37, 46-62 const fileDownloader = new FileDownloader(); // ... socket.on('data', (data: string) => { const remainingData = fileDownloader.buffer(data); // every PTY byte forwarded by the server passes through buffer() // ... }) ``` Every byte the server forwards from the PTY passes through `FileDownloader.buffer`. The buffer scans for the documented file-download markers `\x1b[5i` (begin) and `\x1b[4i` (end) - documented in `docs/downloading-files.md` - and, on a complete match, hands the inner payload to `onCompleteFile`. ```typescript // src/client/wetty/download.ts:9-77 function onCompleteFile(bufferCharacters: string): void { let fileNameBase64; let fileCharacters = bufferCharacters; if (bufferCharacters.includes(':')) { [fileNameBase64, fileCharacters] = bufferCharacters.split(':'); } // ... void detectAndDownload(bytes, fileCharacters, fileNameBase64); } async function detectAndDownload(/* ... */): Promise<void> { // ... let fileName; try { if (fileNameBase64 !== undefined) { fileName = window.atob(fileNameBase64); // attacker-controlled } } catch { /* ... */ } fileName ??= `file-${ /* timestamp default */ }`; // ... Toastify({ text: `Download ready: <a href="${blobUrl}" target="_blan