# CVE-2026-103858: MISP Incomplete Thread Authorization Allows Unauthorized Read and Post Access to Discussions

> Authenticated users can read and post to restricted MISP discussion threads due to incomplete authorization checks, exposing sensitive data and allowing unauthorized content injection.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Oct 2026
- **Updated:** 1 Oct 2026
- **Also known as:** GHSA-vwhj-wmrx-p88c

## What is CVE-2026-103858?

CVE-2026-103858 is a medium-severity missing authorization vulnerability in MISP, published on 1 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

MISP contains an incomplete authorization check in the discussion posting functionality. When a user submits a post to a thread or replies to an existing post, the application only verified whether the target thread was restricted to a single organization (org-only distribution). It did not enforce the full thread access control list, including sharing-group membership and event-level visibility.

As a result, an authenticated user who is outside the relevant sharing group or who does not have visibility on the associated event could:

- Read the thread title and the content of the quoted post

- Submit a new post into the discussion thread

This constitutes both an information disclosure (reading restricted thread and post content) and an integrity issue (injecting content into a thread the user is not authorized to participate in).

Affected: <2.5.48

Weakness: CWE-285 (Improper Authorization)

## Which versions are affected by CVE-2026-103858?


## How do I fix CVE-2026-103858?

No fix has been published for CVE-2026-103858 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103858 being exploited?

There is no known exploitation of CVE-2026-103858 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103858 and fix it if it is affected.

What it is: CVE-2026-103858 is a medium-severity missing authorization vulnerability in MISP, published on 1 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-103858 in the wild and no public exploit code.

Affected product: 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-2026-103858/ (Markdown: https://insights.sbomify.com/CVE-2026-103858/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103858
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103858
- OSV: https://osv.dev/vulnerability/CVE-2026-103858

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103858/
Summaries are generated and may contain mistakes; the official description above is the record.