CVE-2019-16785: HTTP Request Smuggling: LF vs CRLF handling in Waitress

Vulnerability summary

CVE-2019-16785 is a high (CVSS 7.5) vulnerability in agendaless waitress. EPSS estimates a 2.54% chance of exploitation in the next 30 days, higher than 84.9% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 20-12-2019
   PublishedVulnerability first disclosed.
2. 05-08-2024
   Last modifiedVulnerability information updated.

Description

Waitress through version 1.3.1 implemented a "MAY" part of the RFC7230 which states: "Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient MAY recognize a single LF as a line terminator and ignore any preceding CR." Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message. This issue is fixed in Waitress 1.4.0.

• CWE-444Inconsistent Interpretation of HTTP RequestsThe product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.