# CVE-2026-91999: Apache Sling XSS: Improper escaping in the XSS Webconsole plugin

> An attacker can execute arbitrary scripts in the victim's browser via improper escaping in the Apache Sling XSS Webconsole plugin.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **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:** 23 Sep 2026
- **Updated:** 23 Sep 2026
- **Also known as:** GHSA-p3rj-cf34-r824

## What is CVE-2026-91999?

CVE-2026-91999 is a medium-severity cross-site scripting vulnerability in Apache Sling XSS, published on 23 Sep 2026. 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

Improper neutralization of input during web page generation ('cross-site scripting') vulnerability in Apache Sling XSS.

This issue affects Apache Sling XSS: before 2.4.12.

Users are recommended to upgrade to version 2.4.12, which fixes the issue.

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

## Which versions are affected by CVE-2026-91999?

It affects 1 product.


Products: Apache Sling Xss Protection Api.

## How do I fix CVE-2026-91999?

No fix has been published for CVE-2026-91999 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-91999 being exploited?

There is no known exploitation of CVE-2026-91999 in the wild and no public exploit code.

## Other vulnerabilities in Apache Sling XSS

- [CVE-2026-73192](https://insights.sbomify.com/CVE-2026-73192/): Apache Sling XSS: XSS possible through XSSAPI.getValidHref() (medium 6.1)
- [CVE-2026-91852](https://insights.sbomify.com/CVE-2026-91852/): Apache Sling XSS: CWE-79 multiple raw-string break-outs and ReDOS in XSSImpl (medium 6.1)
- [CVE-2026-91928](https://insights.sbomify.com/CVE-2026-91928/): Apache Sling XSS: Sanitizer bypass, uncontrolled resource consumption and failure pf protection mechanisms (medium 6.1)
- [CVE-2026-92001](https://insights.sbomify.com/CVE-2026-92001/): Apache Sling XSS: Missing parser resource limits (medium 6.1)
- [CVE-2017-15717](https://insights.sbomify.com/CVE-2017-15717/): Cross-site Scripting in Apache Sling XSS Protection API (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91999 and fix it if it is affected.

What it is: CVE-2026-91999 is a medium-severity cross-site scripting vulnerability in Apache Sling XSS, published on 23 Sep 2026. 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-2026-91999 in the wild and no public exploit code.

Affected product: Apache Sling XSS. 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-2026-91999/ (Markdown: https://insights.sbomify.com/CVE-2026-91999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91999
- OSV: https://osv.dev/vulnerability/CVE-2026-91999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91999/
Summaries are generated and may contain mistakes; the official description above is the record.