CVE-2026-45372

cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection

State: Published
Severity: 9.9 Critical
Published: May 29, 2026
Updated: Jun 1, 2026
Reserved: May 12, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	9.9 Critical	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L	GitHub_M

Weaknesses

CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')
CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Affected Products

Product	Versions
cpp-httplibyhirose	< 0.44.0Affected

References

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-xjxg-64p4-vj4m

Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.