Better Auth's multi-session sign-out hook allows forged cookies to revoke arbitrary sessions
Summary
A vulnerability was identified in the multi-session plugin for Better Auth, specifically in the /sign-out after-hook. The hook trusts raw multi-session cookies and forwards the extracted values directly to internalAdapter.deleteSessions without verifying the cookie signature. Because cookie values are not validated with getSignedCookie (or any equivalent check), an attacker can supply a forged _multi-* cookie to trigger deletion of arbitrary session tokens.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | better-auth | >= 1.3.34, < 1.4.0 | 1.4.0 |
References
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:L/VI:L/VA:L/SC:L/SI:L/SA:N- Weakness (CWE)
CWE-287, CWE-345- Platform
- npm
- Package
better-auth- Disclosed
- 26.11.2025
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-wmjr-v86c-m9jj - CC BY 4.0
Vulnerability history: better-auth
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 22
- First → latest
- 12.2024 07.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- High 14
- Medium 3
- Low 3
Disclosures per year
- 2024: 1
- 2025: 8
- 2026: 13
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Better Auth's multi-session sign-out hook allows forged cookies to revoke arbitrary sessions this entry
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