Headline
CVE-2023-42452: Stored XSS through the translation feature
Mastodon is a free, open-source social network server based on ActivityPub. In versions on the 4.x branch prior to versions 4.0.10, 4.2.8, and 4.2.0-rc2, under certain conditions, attackers can abuse the translation feature to bypass the server-side HTML sanitization, allowing unescaped HTML to execute in the browser. The impact is limited thanks to Mastodon’s strict Content Security Policy, blocking inline scripts, etc. However a CSP bypass or loophole could be exploited to execute malicious XSS. Furthermore, it requires user interaction, as this can only occur upon clicking the “Translate” button on a malicious post. Versions 4.0.10, 4.2.8, and 4.2.0-rc2 contain a patch for this issue.
Summary
Under certain conditions, attackers can abuse the translation feature to bypass the server-side HTML sanitization, allowing unescaped HTML to execute in the browser.
Details
TBA. This advisory will be edited with more details on 2023/10/02, when admins have been given some time to update, as we think any amount of detail would make it easier to come up with an exploit.
Impact
The impact is limited thanks to Mastodon’s strict Content Security Policy, blocking inline scripts, etc. However a CSP bypass or loophole could be exploited to execute malicious XSS,
Furthermore, it requires user interaction, as this can only occur upon clicking the “Translate” button on a malicious post.