CVE-2026-40470 CRITICAL

CVE-2026-40470: Hackage package and doc upload stored XSS vulnerability

Weakness CWE-79 · XSS
Published April 23, 2026
Last update April 23, 2026

CVSS base score

9.9/10
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Confidentiality High
Integrity High

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

April 23, 2026 CVE published
April 23, 2026 Record updated