# CVE-2025-55035: Mattermost Desktop DoS when user has basic authentication server configured

> An attacker can deny service to Mattermost Desktop users by forcing an unclosable modal popup when a malicious server with basic authentication is configured.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 16 Oct 2025
- **Updated:** 16 Oct 2025
- **Also known as:** GHSA-3359-25fv-h37v

## What is CVE-2025-55035?

CVE-2025-55035 is a medium-severity denial of service vulnerability in Mattermost, published on 16 Oct 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Mattermost Desktop App versions <=5.13.0 fail to manage modals in the Mattermost Desktop App that stops a user with a server that uses basic authentication from accessing their server which allows an attacker that provides a malicious server to the user to deny use of the Desktop App via having the user configure the malicious server and forcing a modal popup that cannot be closed.

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

## Which versions are affected by CVE-2025-55035?

It affects 1 product.


Products: Mattermost Mattermost Desktop.

## How do I fix CVE-2025-55035?

No fix has been published for CVE-2025-55035 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-55035 being exploited?

There is no known exploitation of CVE-2025-55035 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-2025-55035 and fix it if it is affected.

What it is: CVE-2025-55035 is a medium-severity denial of service vulnerability in Mattermost, published on 16 Oct 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2025-55035 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-2025-55035/ (Markdown: https://insights.sbomify.com/CVE-2025-55035/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-55035
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-55035
- OSV: https://osv.dev/vulnerability/CVE-2025-55035

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-55035/
Summaries are generated and may contain mistakes; the official description above is the record.