CVE-2026-40471

hackage-server lacked Cross-Site Request Forgery (CSRF) protection across its endpoints. Scripts on foreign sites could trigger requests to hackage server, possibly abusing latent credentials to upload packages or perform other administrative actions. Some unauthenticated actions could also be abused (e.g. creating new user accounts).

hackage-server lacked Cross-Site Request Forgery (CSRF) protection across its endpoints. Scripts on foreign sites could trigger requests to hackage server, possibly abusing latent credentials to upload packages or perform other administrative actions. Some unauthenticated actions could also be abused (e.g. creating new user accounts).

hackage-server lacked Cross-Site Request Forgery (CSRF) protection across its endpoints. Scripts on foreign sites could trigger requests to hackage server, possibly abusing latent credentials to upload packages or perform other administrative actions. Some unauthenticated actions could also be abused (e.g. creating new user accounts).

hackage-server lacked Cross-Site Request Forgery (CSRF) protection across its endpoints. Scripts on foreign sites could trigger requests to hackage server, possibly abusing latent credentials to upload packages or perform other administrative actions. Some unauthenticated actions could also be abused (e.g. creating new user accounts).

Hackage CSRF vulnerability

• Vulnerable File: src/Distribution/Server/Features/Votes.hs (example)
• Impact: can forge requests through XSS

hackage-server lacked Cross-Site Request Forgery (CSRF) protection across its endpoints. Scripts on foreign sites could trigger requests to hackage server, possibly abusing latent credentials to upload packages or perform other administrative actions. Some unauthenticated actions could also be abused (e.g. creating new user accounts).

To fix the issue, a new CSRF middleware checks all requests. Requests using HTTP methods other than GET, HEAD and OPTIONS are subject to a check of the Sec-Fetch-Site header, which is widely supported by modern browsers. Cross-site requests are 403 Forbidden. Certain approved and expected non-browser user agents (e.g. cabal-install/*) are exempted from the check, as are requests using token authentication (Authorization: X-ApiKey ...).

The fix has been committed and deployed on hackage.haskell.org.

Acknowledgements

• Joshua Rogers (https://joshua.hu/) of AISLE (https://aisle.com/) reported the issue to the Haskell Security Response Team.
• Spenser Janssen implemented the fix, and Fraser Tweedale reviewed it.
• Gershom Bazerman merged the fix and deployed it to hackage.haskell.org.