CVE-2025-66577 cpp-httplib Untrusted HTTP Header Handling: X-Forwarded-For/X-Real-IP Trust
Attackers can spoof client IP addresses via HTTP headers, poisoning logs and potentially bypassing IP-based authorization checks in applications using cpp-httplib.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-66577?
CVE-2025-66577 is a medium-severity vulnerability in yhirose cpp-httplib, published on 5 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.27.0, a vulnerability allows attacker-controlled HTTP headers to influence server-visible metadata, logging, and authorization decisions. An attacker can supply X-Forwarded-For or X-Real-IP headers which get accepted unconditionally by get_client_ip() in docker/main.cc, causing access and error logs (nginx_access_logger / nginx_error_logger) to record spoofed client IPs (log poisoning / audit evasion). This vulnerability is fixed in 0.27.0.
Which versions are affected by CVE-2025-66577?
It affects 1 product.
Products include Yhirose Cpp-Httplib.
How do I fix CVE-2025-66577?
Upgrade to a fixed version.
Is CVE-2025-66577 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-66577 exists.
Other vulnerabilities in yhirose cpp-httplib
- CVE-2025-66570 cpp-httplib Untrusted HTTP Header Handling: Internal Header Shadowing (REMOTE*/LOCAL*)
- CVE-2026-45372 cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection
- CVE-2026-46527 Null dereference in cpp-httplib
- CVE-2026-32627 cpp-httplib has a Silent TLS Certificate Verification Bypass on HTTPS Redirect via Proxy
- CVE-2026-22776 cpp-httplib vulnerable to a denial of service (DOS) using a zip bomb
Sources
Also known as DEBIAN-CVE-2025-66577, ECHO-ee91-3948-5c74, GHSA-gfpf-r66f-5mh2, UBUNTU-CVE-2025-66577.