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Fencer Vulns
critical 9.9

CVE-2026-45372 json

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

published 2026-05-29 5 mo ago modified 2026-07-22 3 mo 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

  • 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

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
5 mo ago

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-08).

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 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.