CVE-2025-66570 cpp-httplib Untrusted HTTP Header Handling: Internal Header Shadowing (REMOTE*/LOCAL*)
Attackers can spoof IP addresses and bypass authorization by injecting internal HTTP headers that shadow server-generated metadata in 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-2025-66570?
CVE-2025-66570 is a critical 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 inject headers named REMOTE_ADDR, REMOTE_PORT, LOCAL_ADDR, LOCAL_PORT that are parsed into the request header multimap via read_headers() in httplib.h (headers.emplace), then the server later appends its own internal metadata using the same header names in Server::process_request without erasing duplicates. Because Request::get_header_value returns the first entry for a header key (id == 0) and the client-supplied headers are parsed before server-inserted headers, downstream code that uses these header names may inadvertently use attacker-controlled values. Affected files/locations: cpp-httplib/httplib.h (read_headers, Server::process_request, Request::get_header_value, get_header_value_u64) and cpp-httplib/docker/main.cc (get_client_ip, nginx_access_logger, nginx_error_logger). Attack surface: attacker-controlled HTTP headers in incoming requests flow into the Request.headers multimap and into logging code that reads forwarded headers, enabling IP spoofing, log poisoning, and authorization bypass via header shadowing. This vulnerability is fixed in 0.27.0.
Which versions are affected by CVE-2025-66570?
It affects 1 product.
Products include Yhirose Cpp-Httplib.
How do I fix CVE-2025-66570?
Upgrade to a fixed version.
Is CVE-2025-66570 being exploited?
There is no known exploitation of CVE-2025-66570 in the wild and no public exploit code.
Other vulnerabilities in yhirose cpp-httplib
- 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
- CVE-2026-21428 cpp-httplib has CRLF injection in http headers
Sources
Also known as DEBIAN-CVE-2025-66570, ECHO-ca5e-a5a0-245b, GHSA-xm2j-vfr9-mg9m, UBUNTU-CVE-2025-66570, USN-7962-1.