Improper Authentication in Mastodon - #VU159853
Published: November 6, 2026
Vulnerability identifier: #VU159853
CSH Severity: Low
CVSS v4: 7.6 [CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-287
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an attacker with a valid local account to bypass password authentication and access another inactive local account in Mastodon.
The vulnerability exists due to login logic allowing account switching mid-login without password verification, triggering a sign-in token email. An attacker with a valid local account can brute-force the six-character base64 token to access accounts with no activity within the past three months and no second-factor authentication.
Affected software
Mastodon
Remediation
Install security update from vendor's website.
Mastodon - update to 4.7.5