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Fencer Intel
critical 9.9

CVE-2026-45372 json

cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection

published 5mo ago modified 3mo ago also EUVD-2026-33427

cvss
9.9
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 22%
public exploits
0
none known

Summary

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.44.0, when cpp-httplib's server parses an incoming request, it applies percent-decoding to every header value except Location and Referer. The validity check (is_field_value) is run before decoding, so encoded %0D%0A passes the check and is then expanded to a literal \r\n byte pair inside the stored header value. This vulnerability is fixed in 0.44.0.

Patch / fix

  • cpp-httplib_project cpp-httplib 0.44.0
  • yhirose cpp-httplib 0.44.0
  • cpp-httplib Ubuntu 25.10 0.18.7-1ubuntu0.25.10.2
  • cpp-httplib Ubuntu Pro 22.04 LTS 0.10.3+ds-1ubuntu0.1~esm2
  • cpp-httplib Ubuntu Pro 24.04 LTS 0.14.3+ds-1.1ubuntu0.1~esm2
  • cpp-httplib Ubuntu Pro 26.04 LTS 0.26.0+ds-2ubuntu3+esm1

ubuntu advisories UBUNTU-CVE-2026-45372

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 openSUSE Tumbleweed 0.46.1-1.1

opensuse advisories openSUSE-SU-2026:10994-1

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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-2026-45372 updated cvss 9.9

cpp-httplib: cpp-httplib: Arbitrary code execution via improper HTTP header processing

  • 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
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
5mo ago

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-xjxg-64p4-vj4m referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 9.9 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:L

Affected products

  • yhirose cpp-httplib

Classification

Weakness
  • CWE-93 Improper Neutralization of CRLF Sequences
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Intel 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.