CVE-2023-42452: Joinmastodon Mastodon

Medium severity, CVSS 5.4. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Joinmastodon Mastodon: from 4.0.0, before 4.0.10 (fixed in 4.0.10); from 4.1.0, before 4.1.8 (fixed in 4.1.8); version 4.2.0 only

Published 2023-09-19. Last modified 2026-06-17.