CVE-2026-21428: Yhirose Cpp-Httplib

High severity, CVSS 7.5. EPSS: 0.4% chance of exploitation in the next 30 days.

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to version 0.30.0, the ``write_headers`` function does not check for CR & LF characters in user supplied headers, allowing untrusted header value to escape header lines. This vulnerability allows attackers to add extra headers, modify request body unexpectedly & trigger an SSRF attack. When combined with a server that supports http1.1 pipelining (springboot, python twisted etc), this can be used for server side request forgery (SSRF). Version 0.30.0 fixes this issue.

Affected products

• Yhirose Cpp-Httplib: before 0.30.0 (fixed in 0.30.0)

Published 2026-01-01. Last modified 2026-06-17.