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Fencer Vulns
critical 10.0

CVE-2025-66570 json

cpp-httplib Untrusted HTTP Header Handling: Internal Header Shadowing (REMOTE*/LOCAL*)

published 2025-12-05 11 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-201455

cvss
10.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 28%
public exploits
0
none known

Summary

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.

Patch / fix

  • cpp-httplib_project cpp-httplib 0.27.0
  • yhirose cpp-httplib 0.27.0
  • cpp-httplib Debian 14 0.41.0+ds-3

debian advisories DEBIAN-CVE-2025-66570

  • cpp-httplib Ubuntu 25.10 0.18.7-1ubuntu0.25.10.1
  • cpp-httplib Ubuntu Pro 22.04 LTS 0.10.3+ds-1ubuntu0.1~esm1
  • cpp-httplib Ubuntu Pro 24.04 LTS 0.14.3+ds-1.1ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2025-66570

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • cpp-httplib SLES for SAP applications 16.0, SLES 16.0 0.22.0-160000.3.1

suse advisories SUSE-SU-2026:20090-1

  • cpp-httplib openSUSE Leap 16.0 0.22.0-160000.3.1
  • cpp-httplib openSUSE Tumbleweed 0.28.0-1.1

opensuse advisories openSUSE-SU-2026:20056-1openSUSE-SU-2025:15844-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-66570 updated cvss 10.0

cpp-httplib: cpp-httplib Untrusted HTTP Header Handling

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
11 mo ago

Exploit prediction

0.35% chance of exploitation in the next 30 days, higher than 28% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-xm2j-vfr9-mg9m referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • yhirose cpp-httplib

Classification

Weakness
  • CWE-290 Authentication Bypass by Spoofing
  • CWE-345 Insufficient Verification of Data Authenticity
  • CWE-807 Reliance on Untrusted Inputs in a Security Decision

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.