CVE-2026-40470 Hackage package and doc upload stored XSS vulnerability
Stored XSS in Hackage allows attackers to hijack user sessions via malicious package uploads, enabling unauthorized metadata changes and account takeover.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40470?
CVE-2026-40470 is a critical cross-site scripting vulnerability in hackage-server, published on 23 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
A critical XSS vulnerability affected hackage-server and hackage.haskell.org. HTML and JavaScript files provided in source packages or via the documentation upload facility were served as-is on the main hackage.haskell.org domain. As a consequence, when a user with latent HTTP credentials browses to the package pages or documentation uploaded by a malicious package maintainer, their session can be hijacked to upload packages or documentation, amend maintainers or other package metadata, or perform any other action the user is authorised to do.
Weakness: CWE-79
Which versions are affected by CVE-2026-40470?
1 open source package ship an affected version, including hackage-server.
| Package | Affected | Fixed in |
|---|---|---|
hackage-server Hackage | From 0.1 | 0.6 |
How do I fix CVE-2026-40470?
Upgrade hackage-server to 0.6 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-40470 being exploited?
There is no known exploitation of CVE-2026-40470 in the wild and no public exploit code.
Sources
Also known as GHSA-hxp4-rf8g-9mwq, HSEC-2024-0004.