CVE-2023-42452: Mastodon vulnerable to Stored XSS through the translation feature

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-09-19 · updated 2026-06-17
Weakness: CWE-79

Description

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

mastodon: from 4.0.0 before 4.0.10; from 4.1.0 before 4.1.8; 4.2.0-beta1, 4.2.0-beta2, 4.2.0-beta3, 4.2.0-rc1 — fixed in 4.0.10, 4.1.8

How to fix

Upgrade to a fixed version: mastodon 4.0.10, 4.1.8. Check the vendor advisory for mitigations.

References

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