# CVE-2026-86351: MISP open redirect via insufficient homepage validation

Source: https://junglewise.ai/threats/cve-2026-86351-misp-open-redirect-via-insufficient-homepage-validation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-07. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-86351 · Severity: medium · CVSS 6.1 · Published 2026-09-07

MISP is a threat intelligence platform used by organizations to share and analyze security information. The application allows users to configure a custom homepage URL that is used for post-login redirection. A flaw in the URL validation logic permitted attackers to craft protocol-relative URLs (e.g., //attacker.example) that bypass the check, causing the application to redirect users to external attacker-controlled sites after login, enabling phishing or session hijacking attacks.

Technologies: [Misp](https://junglewise.ai/threats/technologies/misp). Vendors: [Misp](https://junglewise.ai/threats/vendors/misp).

## Quick answers

**Is CVE-2026-86351 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-86351 being exploited in the wild.

**How severe is CVE-2026-86351?** Medium severity, with a CVSS score of 6.1, published 7 September 2026.

**Which products and versions are affected?** Misp ≤2.5.45.

**Is there a fix for CVE-2026-86351?** A patch was published on 2026-08-26: Fix committed to repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-86351 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-86351?** Check whether you run Misp at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is an open redirect in the homepage setting validation. MISP validated user-configurable homepage paths by checking only whether they began with a forward slash (/), which is insufficient because protocol-relative URLs like //attacker.example also start with / but resolve to an external origin in browsers. The vulnerable homepage value is stored in user settings and later retrieved by post-login routing logic, which emits the unvalidated path to the Location HTTP header. The fix implements a comprehensive InternalRedirectValidator that rejects URLs containing a host, scheme, userinfo, unsafe leading sequences (//, /\), malformed URLs, and control characters, with revalidation on read to catch legacy unsafe values.

## Affected products

- MISP MISP ≤2.5.45

## Timeline

- 2026-09-07: disclosed: Published on NVD
- 2026-08-26: patched: Fix committed to repository

## References

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

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