# CVE-2026-86351

## Summary

- **CVE ID:** CVE-2026-86351
- **Severity:** MEDIUM
- **CVSS Score:** 5.1 (CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N)
- **CWE:** CWE-601, CWE-20
- **Published:** Sep 7, 2026
- **Last Modified:** Sep 8, 2026

## Description

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

## Affected Products

- MISP — MISP (0)

## References

- [CNA](https://github.com/MISP/MISP/commit/bd454f65a)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.33%
- **EPSS Percentile:** 25.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._