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CVE-2026-89022 – Authentication Bypass via Social Login Provider Confusion – BookStack before 26.05.

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Summary

CVE-2026-89022 is an authentication bypass vulnerability in BookStack, a self-hosted wiki/documentation platform, caused by improper validation in its social login implementation. The flaw allows an attacker to sign in as an arbitrary user by authenticating through a different social login provider that happens to share the same account ID as the victim, bypassing credential verification entirely. The issue affects all BookStack versions prior to 26.05.5 and carries a CVSS v4.0 base score of 9.1 (Critical).

Technical details

  • Root cause: the SocialAuthService::handleLoginCallback function looks up linked social account records without checking which social provider ("driver") the record belongs to, so accounts from different providers sharing the same provider-assigned user ID are treated as interchangeable.
  • Trigger condition: the BookStack instance must have more than one third-party/social login option enabled (or have had more than one enabled in the past), and an attacker must control or register an account on one of the enabled social providers whose provider-issued ID collides with a victim’s linked account ID on a different provider.
  • Attack vector: network, unauthenticated. The attacker authenticates through their own account on one enabled social provider and is logged into BookStack as the victim user linked to a different provider, without needing the victim’s credentials.
  • Impact: full account takeover of arbitrary BookStack users, including potentially administrative accounts, resulting in unauthorized access to confidentiality- and integrity-sensitive data and functionality within the wiki.

Affected software

  • BookStack: all versions prior to 26.05.5
  • Only instances with more than one social/third-party login provider enabled (currently or historically) are exploitable.

Severity

  • CVSS v4.0 Base Score: 9.1 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade BookStack to version 26.05.5 or later, which scopes social account lookups to the specific social login system used.
  • If upgrading is not immediately possible: disable all but one social/third-party login provider on the instance, or disable social login entirely until the patch can be applied. Note that instances which have ever had more than one social login option enabled should still upgrade, as previously linked accounts may remain exploitable.

References

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