CVE-2026-45372: Yhirose Cpp-Httplib

Critical severity, CVSS 9.9. 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 0.44.0, when cpp-httplib's server parses an incoming request, it applies percent-decoding to every header value except Location and Referer. The validity check (is_field_value) is run before decoding, so encoded %0D%0A passes the check and is then expanded to a literal \r\n byte pair inside the stored header value. This vulnerability is fixed in 0.44.0.

Affected products

• Yhirose Cpp-Httplib: before 0.44.0 (fixed in 0.44.0)

Published 2026-05-29. Last modified 2026-07-22.