🚨 CVE-2026-86351
Affected versions of MISP validate the user-configurable homepage by checking only whether the supplied path begins with /. That check is insufficient because protocol-relative URLs such as //attacker.example also begin with / but resolve to an external origin in browsers.
The vulnerable homepage value can be stored as a user setting and later used by the post-login routing logic. The commit explicitly identifies //attacker.example as a payload that passed validation and was emitted to the Location header after login.
The fix introduces a shared InternalRedirectValidator that rejects URLs containing a host, scheme, userinfo, unsafe leading // or /\, malformed URLs, and control characters. It also revalidates homepage settings on read so legacy or internally written unsafe values cannot bypass the new storage-time validation.
Version affected: ≤2.5.45
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GitHub
fix: [security] Reject protocol-relative homepage paths · MISP/MISP@bd454f6
- //attacker.example passed the homepage validator and was emitted to Location after login (open redirect)
- as reported by Scottish Government - National Cyber Team
Co-Authored-By: Claude Opus 5...
September 7, 2026 68 1
