Impact

There exists a potential header vulnerability in Traefik's handling of the Connection header. Active exploitation of this issue is unlikely, as it requires that a removed header would lead to a privilege escalation, however, the Traefik team has addressed this issue to prevent any potential abuse.

Details

If you have a chain of Traefik middlewares, and one of them sets a request header Important-Security-Header, then sending a request with the following Connection header will cause it to be removed before the request was sent:

curl 'https://example.com' -H "Connection: Important-Security-Header" -0

In this case, the backend does not see the request header Important-Security-Header.

Patches

Traefik v2.4.x: https://github.com/traefik/traefik/releases/tag/v2.4.13

Workarounds

No.

For more information

If you have any questions or comments about this advisory, open an issue.