# CVE-2026-34161: Chamilo LMS: Stored XSS via Malicious File Upload in Social Post Attachments Leads to Arbitrary JavaScript Execution

> Authenticated users can upload malicious HTML files to social posts, leading to stored XSS that enables session hijacking and account takeover.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 14 Apr 2026
- **Updated:** 16 Apr 2026
- **Also known as:** GHSA-273p-jw9w-3g22

## What is CVE-2026-34161?

CVE-2026-34161 is a medium-severity cross-site scripting vulnerability in Chamilo Chamilo Lms, published on 14 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Chamilo LMS is an open-source learning management system. In versions prior to 2.0.0-RC.3, a Stored Cross-Site Scripting (XSS) vulnerability exists in the social post attachment upload functionality, where an authenticated user can upload a malicious HTML file containing JavaScript via the /api/social_post_attachments endpoint. The uploaded file is served back from the application at the generated contentUrl without sanitization, content type restrictions, or a Content-Disposition: attachment header, causing the JavaScript to execute in the browser within the application's origin. Because the payload is stored server-side and runs in the trusted origin, an attacker can perform session hijacking, account takeover, privilege escalation (if an admin views the link), and arbitrary actions on behalf of the victim. This issue has been fixed in version 2.0.0-RC.3.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-34161?

It affects 1 product.


Products: Chamilo Chamilo Lms.

## How do I fix CVE-2026-34161?

No fix has been published for CVE-2026-34161 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-34161 being exploited?

There is no known exploitation of CVE-2026-34161 in the wild and no public exploit code.

## Other vulnerabilities in Chamilo Chamilo Lms

- [CVE-2025-50187](https://insights.sbomify.com/CVE-2025-50187/): Chamilo: Evaluation of untrusted user input leads to Remote Code Execution (critical 9.8)
- [CVE-2023-34944](https://insights.sbomify.com/CVE-2023-34944/): File upload in n/a (critical 9.8)
- [CVE-2022-27423](https://insights.sbomify.com/CVE-2022-27423/): SQL injection in n/a (critical 9.8)
- [CVE-2021-35414](https://insights.sbomify.com/CVE-2021-35414/): SQL injection in n/a (critical 9.8)
- [CVE-2019-13082](https://insights.sbomify.com/CVE-2019-13082/): File upload in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34161 and fix it if it is affected.

What it is: CVE-2026-34161 is a medium-severity cross-site scripting vulnerability in Chamilo Chamilo Lms, published on 14 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-34161 in the wild and no public exploit code.

Affected product: Chamilo Chamilo Lms. 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-2026-34161/ (Markdown: https://insights.sbomify.com/CVE-2026-34161/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34161
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34161
- OSV: https://osv.dev/vulnerability/CVE-2026-34161

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-34161/
Summaries are generated and may contain mistakes; the official description above is the record.