CGI implementation in Yaws web server versions 1.81 to 2.0.7 is vulnerable to OS command injection.

Last updated 26 August 2025

yaws before 2.0.4 does not attempt to address RFC 3875 section 4.1.18 namespace conflicts and therefore does not protect CGI applications from the presence of untrusted client data in the HTTPPROXY environment variable, which might allow remote attackers to redirect a CGI application's outbound HTTP traffic to an arbitrary proxy server via a crafted Proxy header in an HTTP request, aka an "httpoxy" issue.

Yaws 1.91 has a directory traversal vulnerability in the way certain URLs are processed. A remote authenticated user could use this flaw to obtain content of arbitrary local files via specially-crafted URL request.

Directory traversal vulnerability in Yaws 1.89 allows remote attackers to read arbitrary files via ..\ (dot dot backslash) and other sequences.

Yaws before 1.80 allows remote attackers to cause a denial of service (memory consumption and crash) via a request with a large number of headers.