CVE-2026-53512: better auth Auth Bypass — Fix

Description

Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.11, the legacy oidcProvider and mcp plugins expose OAuth token endpoints whose refresh_token grant authenticates only possession of the bound refreshToken row and matching client_id, without verifying the confidential client's client_secret, allowing an attacker with a valid refresh_token to mint access tokens and rotated refresh tokens through /api/auth/oauth2/token or /api/auth/mcp/token. The @better-auth/oauth-provider package is not affected. This issue is fixed in version 1.6.11.

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CVSS v3.1 Score

9.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0030

Probability of exploitation

0.22%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-287 Improper Authentication

CWE-306 Missing Authentication

CWE-345 CWE-345

CWE-863 Incorrect Authorization

Affected Products

Vendor	Product	Versions
better-auth	better_auth	< 1.6.11

References

Advisories & Patches

https://github.com/better-auth/better-auth/commit/1f2ff4215c4affff0b140b0c0a712c0dde35659c https://github.com/better-auth/better-auth/pull/9576 https://github.com/better-auth/better-auth/security/advisories/GHSA-pw9m-5jxm-xr6h

Other References

https://github.com/better-auth/better-auth/releases/tag/v1.6.11

Frequently Asked Questions

What is CVE-2026-53512? +

Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.11, the legacy oidcProvider and mcp plugins expose OAuth token endpoints whose refresh_token grant authenticates only possession of the bound refreshToken row and matching client_id, without verifying the confidential client's client_secret, allowing an attacker with a valid refresh_token to mint access tokens and rotated refresh tokens through /api/auth/oauth2/token or /api/auth/mcp/token. The @better-auth/oauth-provider package is not affected. This issue is fixed in version 1.6.11. It has a CVSS v3.1 base score of 9.1 (CRITICAL).

How severe is CVE-2026-53512? +

CVE-2026-53512 has a CVSS v3.1 score of 9.1 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0030, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-53512? +

CVE-2026-53512 affects products from better-auth, specifically: better_auth. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-53512? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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