A vulnerability in h11 up to version 0.14.0 allows malformed HTTP/1.1 chunked-encoding bodies to be accepted due to lenient parsing of trailing line terminators. This discrepancy can lead to HTTP request smuggling when combined with a proxy that parses chunked bodies differently. The issue is fixed in h11 version 0.15.0. Exploitation requires both h11 and a proxy to have incompatible parsing bugs.