# CVE-2026-86351: MISP User Homepage Validation Allows Authenticated Open Redirect via Protocol-Relative URL

> Authenticated users can trigger open redirects via protocol-relative URLs in homepage settings, potentially facilitating phishing attacks.

- **Severity:** Medium 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 7 Sep 2026
- **Updated:** 8 Sep 2026
- **Also known as:** GHSA-7q84-h6g5-j34g

## What is CVE-2026-86351?

CVE-2026-86351 is a medium-severity vulnerability in Misp-Project Misp, published on 7 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official 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

Weakness: CWE-601 (URL Redirection to Untrusted Site), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-86351?

It affects 1 product.


Products: Misp-Project Misp.

## How do I fix CVE-2026-86351?

No fix has been published for CVE-2026-86351 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-86351 being exploited?

There is no known exploitation of CVE-2026-86351 in the wild and no public exploit code.

## Other vulnerabilities in Misp-Project Misp

- [CVE-2024-46918](https://insights.sbomify.com/CVE-2024-46918/): Missing authorization in n/a (critical 9.8)
- [CVE-2024-45509](https://insights.sbomify.com/CVE-2024-45509/): Missing authorization in n/a (critical 9.8)
- [CVE-2024-29858](https://insights.sbomify.com/CVE-2024-29858/): File upload in n/a (critical 9.8)
- [CVE-2024-29859](https://insights.sbomify.com/CVE-2024-29859/): File upload in n/a (critical 9.8)
- [CVE-2024-25674](https://insights.sbomify.com/CVE-2024-25674/): File upload in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86351 and fix it if it is affected.

What it is: CVE-2026-86351 is a medium-severity vulnerability in Misp-Project Misp, published on 7 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-86351 in the wild and no public exploit code.

Affected product: Misp-Project Misp. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-86351/ (Markdown: https://insights.sbomify.com/CVE-2026-86351/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86351
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86351
- OSV: https://osv.dev/vulnerability/CVE-2026-86351

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-86351/
Summaries are generated and may contain mistakes; the official description above is the record.