CVE-2026-110863 better-auth CVE debrief

Who should care

Defenders responsible for Better Auth @better-auth/sso deployments should assess exposure and prioritize upgrading to version 1.7.3 or later. This includes operators, platform administrators, vulnerability management teams, and security teams who need to verify exposure, apply patches, and monitor for suspicious activity.

Why it matters

The authentication bypass vulnerability in Better Auth @better-auth/sso before version 1.7.3 allows attackers to sign in as other users, potentially leading to unauthorized access and lateral movement within the affected system. Defenders should prioritize verifying exposure and upgrading to version 1.7.3 or later.

• Potential unauthorized access to user accounts
• Possible lateral movement within the affected system
• Required verification of exposure and remediation priority
• Potential impact on user authentication and authorization mechanisms

Technical summary

The Better Auth @better-auth/sso library before version 1.7.3 contains an authentication bypass vulnerability. An attacker can register a personal SSO provider and sign in as other users by copying a legitimate provider's OIDC issuer or SAML entity ID and asserting a victim's subject or NameID. This vulnerability is caused by the library's account lookup ignoring providerId, allowing attackers to create sessions for victim accounts. Defenders should prioritize verifying exposure of Better Auth @better-auth/sso versions before 1.7.3 and upgrading to 1.7.3 or later.

Defensive priority

Defenders should prioritize verifying exposure of Better Auth @better-auth/sso versions before 1.7.3 and upgrading to 1.7.3 or later.

Recommended defensive actions

• Verify exposure of Better Auth @better-auth/sso versions before 1.7.3
• Upgrade to version 1.7.3 or later
• Monitor for suspicious login activity
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE Program record and NVD vulnerability detail provide official information about the vulnerability. Supplemental sources include a GitHub Security Advisory and a VulnCheck Advisory. The vulnerability has been verified through these sources, and defenders should review the official advisories for affected scope, severity, and vendor guidance.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.