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Better Auth's multi-session sign-out hook allows forged cookies to revoke arbitrary sessionsGHSA-wmjr-v86c-m9jj

Fix: better-auth/better-auth@cfc453a

GHSA-wmjr-v86c-m9jj is a CWE-347 vulnerability in better-auth. A fix is available for better-auth — see the affected versions and patch details below.

Also known asCVE-2025-71402
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 26, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-wmjr-v86c-m9jj.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs19th percentile — riskier than 19% of all scored CVEsHighest risk
0.00%0.26%0.51%0.77%0.2%0.3%0.3%Sep 26Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

894other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
better-authnpm
11.3Mdownloads / week

Description

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 Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmbetter-auth≥ 1.3.34&&< 1.4.01.4.0npm install better-auth@1.4.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for better-auth, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update better-auth to 1.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-wmjr-v86c-m9jj is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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.
O3 Security · Impact-Aware SCA

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Better Auth's multi-session sign-out hook allows forged…