CVE-2026-40470
Critical
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.
SeverityCritical
CVSS9.9
Exploit probability—
ProductHackage-server
PublishedApr 23, 2026
First seenApr 23, 2026
Weakness typeCWE-79Cross-site scripting (XSS)
How to fix
Update
- hackage-server0.6 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| hackage-server | 0.1 ≤ v < 0.6 | 0.6 |
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