# CVE-2026-126498: WriteFreely before 0.17.3 Stored XSS via Unsanitized Post Slug

> Authenticated authors can store script in a post slug that runs for RSS, newsletter and ActivityPub readers; WriteFreely operators should care.

- **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
- **Harmful if only installed:** No
- **Needs a specific call:** No
- **Fix available:** No
- **Published:** 11 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** GHSA-43p2-x762-x6h7, GHSA-cwxm-8ch5-j2vh

## What is CVE-2026-126498?

CVE-2026-126498 is a medium-severity cross-site scripting vulnerability in Musing Studio WriteFreely, published on 11 Nov 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

WriteFreely before 0.17.3 contains a stored cross-site scripting vulnerability that allows authenticated authors to inject HTML by supplying a malicious post slug via the CreatePost API. The raw slug is concatenated into an anchor by augmentReadingDestination() for paid-shortcode posts, executing script for RSS/Atom feed readers, newsletter recipients and ActivityPub viewers.

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

## Which versions are affected by CVE-2026-126498?

An affected version is exposed as installed. No special setting or call is needed.


## How do I fix CVE-2026-126498?

No fix has been published for CVE-2026-126498 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-126498 being exploited?

There is no known exploitation of CVE-2026-126498 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126498 and fix it if it is affected.

What it is: CVE-2026-126498 is a medium-severity cross-site scripting vulnerability in Musing Studio WriteFreely, published on 11 Nov 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-2026-126498 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected product: Musing Studio WriteFreely. 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-2026-126498/ (Markdown: https://insights.sbomify.com/CVE-2026-126498/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126498
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126498
- OSV: https://osv.dev/vulnerability/CVE-2026-126498

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126498/
Summaries are generated and may contain mistakes; the official description above is the record.