# CVE-2023-2787: Collapsed Reply Threads APIs leak message contents from private channels

> Attackers can read private channel messages via the threads API due to missing membership checks in Mattermost.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A: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:** 16 Jun 2023
- **Updated:** 6 Dec 2024
- **Also known as:** GHSA-8m2w-p6c5-hh6c

## What is CVE-2023-2787?

CVE-2023-2787 is a medium-severity missing authorization vulnerability in Mattermost Mattermost, published on 16 Jun 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Mattermost fails to check channel membership when accessing message threads, allowing an attacker to access arbitrary posts by using the message threads API.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2023-2787?

It affects 1 product.


Products: Mattermost Mattermost.

## How do I fix CVE-2023-2787?

No fix has been published for CVE-2023-2787 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-2787 being exploited?

There is no known exploitation of CVE-2023-2787 in the wild and no public exploit code.

## Other vulnerabilities in Mattermost Mattermost

- [CVE-2019-20851](https://insights.sbomify.com/CVE-2019-20851/): Path traversal in n/a (critical 9.1)
- [CVE-2024-39274](https://insights.sbomify.com/CVE-2024-39274/): Malicious remote can add users to arbitrary teams and channels (high 8.7)
- [CVE-2024-39777](https://insights.sbomify.com/CVE-2024-39777/): Malicious remote can invite itself to an arbitrary local channel (high 8.7)
- [CVE-2024-39830](https://insights.sbomify.com/CVE-2024-39830/): Timing attack during remote cluster token comparison when shared channels are enabled (high 8.1)
- [CVE-2023-3615](https://insights.sbomify.com/CVE-2023-3615/): Lack of server certificate validation in websockets connection (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-2787 and fix it if it is affected.

What it is: CVE-2023-2787 is a medium-severity missing authorization vulnerability in Mattermost Mattermost, published on 16 Jun 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-2787 in the wild and no public exploit code.

Affected product: Mattermost 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-2023-2787/ (Markdown: https://insights.sbomify.com/CVE-2023-2787/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-2787
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-2787
- OSV: https://osv.dev/vulnerability/CVE-2023-2787

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-2787/
Summaries are generated and may contain mistakes; the official description above is the record.