Vulnerability · Published May 29, 2026 · Assigned by GitHub_M

CVE-2026-45372cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection

Critical 9.9

In plain English

A critical-severity security flaw in cpp-httplib from yhirose. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.9Critical

Exploit odds (30 days)0.3%top 77.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	cpp-httplib	no fix listed	DEBIAN-CVE-2026-45372
Debian:13	cpp-httplib	no fix listed	DEBIAN-CVE-2026-45372
Debian:14	cpp-httplib	no fix listed	DEBIAN-CVE-2026-45372
Ubuntu:25.10	cpp-httplib	0.18.7-1ubuntu0.25.10.2	USN-8470-1
Ubuntu:25.10	cpp-httplib	0.18.7-1ubuntu0.25.10.2	UBUNTU-CVE-2026-45372
Ubuntu:26.10	cpp-httplib	no fix listed	UBUNTU-CVE-2026-45372

Affected products (as reported)

Vendor	Product	Versions
yhirose	cpp-httplib	< 0.44.0

Weakness: CWE-93, CWE-444 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L

References

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