vproxy Divide by Zero DoS Vulnerability

Summary

Untrusted, user-controlled data from the HTTP Proxy-Authorization header can induce a denial of service state.

Details

Untrusted data is extracted from the user-controlled HTTP Proxy-Authorization header and passed to Extension::try_from and flows into parse_ttl_extension where it is parsed as a TTL value. If an attacker supplies a TTL of zero (e.g. by using a username such as 'configuredUser-ttl-0'), the modulo operation 'timestamp % ttl' will cause a division by zero panic, causing the server to crash causing a denial-of-service.

The code assumed to be responsible for this can be found here: https://github.com/0x676e67/vproxy/blob/ab304c3854bf8480be577039ada0228907ba0923/src/extension.rs#L173-L183

PoC

1. Download and run the latest version of vproxy
2. Send a cUrl request like the following, adjusting address and port as necessary: curl -x "http://test-ttl-0:[email protected]:8101" https://google.com
3. Wait for a cUrl error indicating "Proxy CONNECT aborted"
4. View logs from the vproxy server
5. Observe that the vproxy server crashed due to a divide-by-zero panic

Impact

The resulting crash renders the proxy server unusable until it is reset.

Finally, one last note: I'm reporting this on behalf of another researcher at Black Duck. Credit for discovery should be attributed to David Bohannon (dbohannon)