Vulnerability · Published May 29, 2026 · Assigned by GitHub_M

CVE-2026-46527cpp-httplib: Malicious `X-Forwarded-For` Under Trusted-Proxy Configuration Triggers Empty `vector::front()`, Leading to Undefined Behavior and Server Crash

High 8.7

In plain English

A high-severity null pointer dereference 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 26% of all known vulnerabilities).

Severity (CVSS 4.0)8.7High

Exploit odds (30 days)0.3%top 74.0% 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 the server has called Server::set_trusted_proxies() with a non-empty trusted-proxy list, an attacker can send an HTTP request that includes an X-Forwarded-For header whose value parses to no valid IP segments. The code path then executes get_client_ip(), which calls front() on an empty std::vector—undefined behavior in C++. On typical implementations this manifests as abnormal process termination (denial of service). With Sanitizers enabled, you get an explicit runtime diagnostic. 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-2026-46527
Debian:13	cpp-httplib	no fix listed	DEBIAN-CVE-2026-46527
Debian:14	cpp-httplib	no fix listed	DEBIAN-CVE-2026-46527
Ubuntu:25.10	cpp-httplib	no fix listed	UBUNTU-CVE-2026-46527
Ubuntu:26.10	cpp-httplib	no fix listed	UBUNTU-CVE-2026-46527

Affected products (as reported)

Vendor	Product	Versions
yhirose	cpp-httplib	< 0.44.0

Weakness: CWE-476 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

References

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-hg3g-vrg8-578g x_refsource_CONFIRM