EUVD-2026-78821
GHSA-54r8-f2jx-5qj6
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable and unauthenticated (PR:N), but AC:H because it needs multiple providers with a colliding driver_id namespace; full account takeover gives C:H/I:H, no availability impact.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
4DescriptionCVE.org
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.
AnalysisAI
Authentication bypass in BookStack social login (all versions before 26.05.5) allows unauthenticated attackers to sign in as arbitrary users, enabling full account takeover of both regular accounts and administrators. The flaw is a provider-confusion bug in SocialAuthService::handleLoginCallback, which retrieves linked-account records by driver_id while ignoring the driver column, so an attacker who authenticates at one enabled social provider using a user ID that collides with a victim's driver_id under a different provider is accepted without credential verification. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the BookStack instance to have at least two social login providers enabled that share the same driver_id namespace, because the flaw is that SocialAuthService::handleLoginCallback retrieves linked-account records by driver_id while ignoring the driver column. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | This is a genuine authentication-bypass (CWE-290) enabling full account takeover, and the signals are mostly consistent. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to BookStack 26.05.5, the vendor-released patch for this issue (patch available from vendor; see https://www.bookstackapp.com/blog/bookstack-release-v26-05-5/). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory every BookStack instance and confirm whether more than one social login provider is enabled, since the flaw only succeeds when two enabled providers share an overlapping driver_id namespace; on any system with that configuration, either disable the secondary social provider or fall back to standard credential and SAML-based authentication until the upgrade can be completed, and raise monitoring on authentication events for unexpected provider/user pairings. …
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Same weakness CWE-290 – Authentication Bypass by Spoofing
View allSame technique Authentication Bypass
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External POC / Exploit Code
Leaving vuln.today