# CVE-2026-8075: Posting a malicious markdown image crashes the Mattermost Desktop App

> An attacker can crash a victim's Mattermost Desktop App by posting a malicious markdown image with missing headers, causing a null dereference.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** 17 Jul 2026
- **Updated:** 17 Jul 2026
- **Also known as:** GHSA-rm64-886x-w6qc

## What is CVE-2026-8075?

CVE-2026-8075 is a medium-severity vulnerability in Mattermost, published on 17 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Mattermost Desktop App versions <=6.2 5.5.13 6.0.2.0 fail to properly null check when checking for headers in the Mattermost Desktop App which allows any user to crash another channel members Desktop App via posting a malicious link with an embedded image that misses one of those headers. Mattermost Advisory ID: MMSA-2026-00668

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2026-8075?

It affects 1 product.


Products: Mattermost Mattermost Desktop.

## How do I fix CVE-2026-8075?

No fix has been published for CVE-2026-8075 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-8075 being exploited?

There is no known exploitation of CVE-2026-8075 in the wild and no public exploit code.

## Other vulnerabilities in Mattermost

- [CVE-2016-11064](https://insights.sbomify.com/CVE-2016-11064/): Code injection in n/a (critical 9.8)
- [CVE-2019-20856](https://insights.sbomify.com/CVE-2019-20856/): Code injection in n/a (critical 9.8)
- [CVE-2019-20861](https://insights.sbomify.com/CVE-2019-20861/): Code injection in n/a (high 8.8)
- [CVE-2026-1046](https://insights.sbomify.com/CVE-2026-1046/): Arbitrary application execution via unvalidated server-controlled URLs in Help menu (high 7.6)
- [CVE-2020-14456](https://insights.sbomify.com/CVE-2020-14456/): Security feature bypass in n/a (high 7.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-8075 and fix it if it is affected.

What it is: CVE-2026-8075 is a medium-severity vulnerability in Mattermost, published on 17 Jul 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-2026-8075 in the wild and no public exploit code.

Affected product: Mattermost. 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-2026-8075/ (Markdown: https://insights.sbomify.com/CVE-2026-8075/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8075
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8075
- OSV: https://osv.dev/vulnerability/CVE-2026-8075

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-8075/
Summaries are generated and may contain mistakes; the official description above is the record.