# CVE-2026-16889: Stored XSS via Pre-Login Notice Image Upload Serves Attacker HTML from Application Origin


- **Severity:** Medium 4.8 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 29 Oct 2026
- **Updated:** 29 Oct 2026
- **Also known as:** GHSA-jj9r-xgj6-prvj, GHSA-q2xv-rffq-mj5w

## What is CVE-2026-16889?

CVE-2026-16889 is a medium-severity vulnerability in Apereo Foundation openEQUELLA, published on 29 Oct 2026. 

### Official description

In openEQUELLA before 2026.1, the pre-login notice image upload endpoint (PUT /api/preloginnotice/image/{name}) does not validate the type of uploaded files and serves them with a Content-Type derived from the supplied filename. A user holding the EDIT_SYSTEM_SETTINGS permission can upload an HTML file that is then served as text/html from the openEQUELLA origin, resulting in stored cross-site scripting. Unauthenticated exploitation is possible where EDIT_SYSTEM_SETTINGS has been granted to the guest user or everyone.

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

## Which versions are affected by CVE-2026-16889?


## How do I fix CVE-2026-16889?

No fix has been published for CVE-2026-16889 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-16889 being exploited?

There is no known exploitation of CVE-2026-16889 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-16889 and fix it if it is affected.

What it is: CVE-2026-16889 is a medium-severity vulnerability in Apereo Foundation openEQUELLA, published on 29 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-16889 in the wild and no public exploit code.

Affected product: Apereo Foundation openEQUELLA. 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-2026-16889/ (Markdown: https://insights.sbomify.com/CVE-2026-16889/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-16889
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-16889
- OSV: https://osv.dev/vulnerability/CVE-2026-16889

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-16889/
Summaries are generated and may contain mistakes; the official description above is the record.