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Fencer Vulns
medium 6.3

CVE-2026-63379 json

Libevent: HTTP Header smuggling

published 2026-08-20 2 mo ago modified 2026-10-26 14 d ago also EUVD-2026-63562

cvss
6.3
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent processes chunked HTTP trailers in http.c through evhttp_read_trailer and merges them into request headers. The fix introduces evhttp_parse_headers_impl_ and a temporary trailer header list. An unauthenticated remote attacker can place security-sensitive fields in trailers so that an upstream proxy and the libevent application interpret different effective headers, enabling header smuggling, authorization bypass, proxy-header spoofing, or cache poisoning. The fix parses trailers into a temporary header list and discards them instead of merging them into req->input_headers. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Patch / fix

  • libevent_project libevent 2.1.13, 2.2.2-alpha
  • libevent Debian 12 2.1.12-stable-8+deb12u1
  • libevent Debian 13 2.1.13-stable-1~deb13u1
  • libevent Debian 14 2.1.13-stable-1

debian advisories DEBIAN-CVE-2026-63379

  • libevent RHEL 9 2.1.13-1.el9_8
  • libevent RHEL 10.2 2.1.13-1.el10_2
  • libevent hummingbird 1 2.1.12-19.1.hum1

red hat advisories RHSA-2026:67910RHSA-2026:67909RHSA-2026:60853

  • libevent openSUSE Tumbleweed 2.1.13-1.1

opensuse advisories openSUSE-SU-2026:12330-1

  • libevent AlmaLinux 10 2.1.13-1.el10_2
  • libevent AlmaLinux 9 2.1.13-1.el9_8

almalinux advisories ALSA-2026:67909ALSA-2026:67910

  • libevent Rocky Linux 10 2.1.13-1.el10_2
  • libevent Rocky Linux 9 2.1.13-1.el9_8

rocky linux advisories RLSA-2026:67909RLSA-2026:67910

  • libevent Azure Linux 3.0 2.1.13-1
  • mysql Azure Linux 3.0 8.0.46-2
  • ntp Azure Linux 3.0 4.2.8p17-3

azure linux advisories AZL-96941AZL-97533AZL-97557

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2026-63379 updated cvss 6.5

libevent: Libevent: HTTP header smuggling allows authorization bypass or cache poisoning

  • Red Hat Enterprise Linux 6 libevent 1.4.13-4.el6, libevent2 2.0.21-2.el6
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 libevent 1.4.13-4.el6 Red Hat Enterprise Linux 8 libevent, libevent 1.4.13-4.el6 Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/cert-manager-operator-rhel9 1790272426, cert-manager/cert-manager-operator-rhel9 1790589855, cert-manager/jetstack-cert-manager-rhel9 1790223279, cert-manager/jetstack-cert-manager-rhel9 1790589912, cert-manager/cert-manager-istio-csr-rhel9 1790223719, cert-manager/cert-manager-istio-csr-rhel9 1790589914, +1 more
    fixed: vendor fix RHSA-2026:72475
  • Red Hat Enterprise Linux AppStream (v. 9) libevent-doc 2.1.13-1.el9_8, libevent-devel 2.1.13-1.el9_8, libevent-debuginfo 2.1.13-1.el9_8, libevent-debugsource 2.1.13-1.el9_8
    fixed: vendor fix RHSA-2026:67910
  • Red Hat Enterprise Linux AppStream (v. 10) libevent-doc 2.1.13-1.el10_2, libevent-devel 2.1.13-1.el10_2, libevent-debuginfo 2.1.13-1.el10_2, libevent-debugsource 2.1.13-1.el10_2
    fixed: vendor fix RHSA-2026:67909
  • Red Hat Enterprise Linux BaseOS (v. 9) libevent 2.1.13-1.el9_8
    fixed: vendor fix RHSA-2026:67910
  • Red Hat Enterprise Linux BaseOS (v. 10) libevent 2.1.13-1.el10_2
    fixed: vendor fix RHSA-2026:67909
  • Red Hat Hardened Images libevent 2.1.12-19.1.hum1
    fixed: vendor fix RHSA-2026:60853
show 2 more
  • Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1790241954, rhui5/rhua-rhel9 1790242004, rhui5/haproxy-rhel9 1790241900, rhui5/installer-rhel9 1790241922, rhui5/cds-kubernetes-rhel9 1790241897
    fixed: vendor fix RHSA-2026:71603
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/jetstack-cert-manager-acmesolver-rhel9 1790223630 Red Hat OpenShift AI (RHOAI) rhoai/odh-llama-stack-k8s-operator-rhel9
    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
partial
Assessed
2 mo ago

Exploit prediction

0.52% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

  • libevent libevent

Classification

Weakness
  • 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.

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