# CVE-2021-26918: File upload in n/a

> Attackers can upload malicious files with double extensions to the Discord bot's uploader, potentially enabling code execution or bypassing security controls.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-ghmj-xphc-2mq4

## What is CVE-2021-26918?

CVE-2021-26918 is a critical vulnerability in n/a, published on 9 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The ProBot bot through 2021-02-08 for Discord might allow attackers to interfere with the intended purpose of the "Send an image when a user joins the server" feature (or possibly have unspecified other impact) because the uploader web service allows double extensions (such as .html.jpg) with the text/html content type. NOTE: there may not be cases in which an uploader web service is customer controlled; however, the nature of the issue has substantial interaction with customer controlled configuration. NOTE: the vendor states "This is just an uploader (like any other one) which uploads files to cloud storage and accepts various file types. There is no kind of vulnerability and it won't compromise either the client side or the server side.

Weakness: CWE-434 (Unrestricted Upload of File with Dangerous Type)

## Which versions are affected by CVE-2021-26918?

It affects 1 product.


Products: Probot Bot.

## How do I fix CVE-2021-26918?

No fix has been published for CVE-2021-26918 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-26918 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-26918 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-26918 and fix it if it is affected.

What it is: CVE-2021-26918 is a critical vulnerability in n/a, published on 9 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-26918 exists.

Affected product: n/a. 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-2021-26918/ (Markdown: https://insights.sbomify.com/CVE-2021-26918/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26918
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26918
- OSV: https://osv.dev/vulnerability/CVE-2021-26918

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-26918/
Summaries are generated and may contain mistakes; the official description above is the record.