CVE-2026-110863

High

Description

Better Auth @better-auth/sso from 1.7.0-rc.2 before 1.7.3 contains an authentication bypass vulnerability that allows authenticated users to sign in as other users by registering a personal SSO provider. Attackers can copy a legitimate provider's OIDC issuer or SAML entity ID and assert a victim's subject or NameID, because account lookup ignores providerId, creating sessions for victim accounts.

SeverityHigh

CVSS8.1

Exploit probability—

ProductBetter-auth Sso

PublishedOct 14, 2026

First seenOct 14, 2026

Weakness typeCWE-287Improper authentication

How to fix

Update

better-auth sso1.7.3 or later

Vendor advisories

github.com/better-auth/better-auth/security/advisories/GHSA-mx9r-x6ww-qjw9

Affected products

Product	Affected versions	Fixed in
better-auth sso	1.7.0-rc.2 ≤ v < 1.7.3	1.7.3

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