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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2025-66570)

The remote Fedora 42 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-3b0e5b457d advisory.

    # Update to 0.30.1

    - [Denial of service (DOS) using zip bomb (CVE-2026-22776)](https://github.com/yhirose/cpp-     httplib/security/advisories/GHSA-h934-98h4-j43q)
    - [CRLF injection in http headers (CVE-2026-21428)](https://github.com/yhirose/cpp-     httplib/security/advisories/GHSA-wpc6-j37r-jcx7)
    - [Untrusted HTTP Header Handling: X-Forwarded-For/X-Real-IP Trust     (CVE-2025-66577)](https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-gfpf-r66f-5mh2)

    https://github.com/yhirose/cpp-httplib/releases/tag/v0.30.1

Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-e50e41fcea advisory.

    # Update to 0.30.1

    - [Denial of service (DOS) using zip bomb (CVE-2026-22776)](https://github.com/yhirose/cpp-     httplib/security/advisories/GHSA-h934-98h4-j43q)
    - [CRLF injection in http headers (CVE-2026-21428)](https://github.com/yhirose/cpp-     httplib/security/advisories/GHSA-wpc6-j37r-jcx7)
    - [Untrusted HTTP Header Handling: X-Forwarded-For/X-Real-IP Trust     (CVE-2025-66577)](https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-gfpf-r66f-5mh2)

    https://github.com/yhirose/cpp-httplib/releases/tag/v0.30.1


Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Ubuntu 22.04 LTS / 24.04 LTS / 25.10 host has packages installed that are affected by a vulnerability as referenced in the USN-7962-1 advisory.

    It was discovered that cpp-httplib did not correctly handle

    HTTP headers. A remote attacker could possibly use this

    issue to bypass authorization and impersonate users.

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The remote openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:20056-1 advisory.

    - CVE-2025-66570: IP spoofing, log poisoning, and authorization bypass via header shadowing due to     acceptance and       parsing of client-controlled injected HTTP headers in incoming requests (bsc#1254734).
    - CVE-2025-66577: access and error log poisoning with spoofed client IPs due to unconditional acceptance     of       client-controlled `X-Forwarded-For` and `X-Real-IP` headers (bsc#1254735).

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2025-66570)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
461631	Echo: cpp-httplib: security update to 0.18.7-1+e2	Tenable Cloud Security	Echo Local Security Checks	Local	critical
461631	Echo: cpp-httplib: security update to 0.18.7-1+e2	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	critical
294951	Fedora 42 : cpp-httplib (2026-3b0e5b457d)	Nessus	Fedora Local Security Checks	Local	high
294942	Fedora 43 : cpp-httplib (2026-e50e41fcea)	Nessus	Fedora Local Security Checks	Local	high
294843	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 : cpp-httplib vulnerability (USN-7962-1)	Nessus	Ubuntu Local Security Checks	Local	critical
291337	openSUSE 16 Security Update : cpp-httplib (openSUSE-SU-2026:20056-1)	Nessus	SuSE Local Security Checks	Local	critical
277659	Linux Distros Unpatched Vulnerability : CVE-2025-66570	Nessus	Misc.	Local	critical

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CVE-2025-66570

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