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Fencer Intel
medium 5.3

CVE-2026-4271 json

Libsoup: libsoup: denial of service via use-after-free in http/2 server

published 7mo ago modified 4d ago also EUVD-2026-12568

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 59%
public exploits
0
none known

Summary

A flaw was found in libsoup, a library for handling HTTP requests. This vulnerability, known as a Use-After-Free, occurs in the HTTP/2 server implementation. A remote attacker can exploit this by sending specially crafted HTTP/2 requests that cause authentication failures. This can lead to the application attempting to access memory that has already been freed, potentially causing application instability or crashes, resulting in a Denial of Service (DoS).

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 0:3.6.5-3.el10_1.11, 0:3.6.5-3.el10_2.11
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support 0:3.6.5-3.el10_0.15
  • libsoup3 Ubuntu 24.04 LTS 3.4.4-5ubuntu0.9
  • libsoup3 Ubuntu 26.10 3.6.6-1ubuntu3
  • libsoup3 Ubuntu 26.04 LTS 3.6.6-1ubuntu0.1

ubuntu advisories UBUNTU-CVE-2026-4271

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

  • libsoup3 RHEL 10.2 3.6.5-3.el10_2.11
  • libsoup3 RHEL 10.1 3.6.5-3.el10_1.11
  • libsoup3 enterprise linux eus 10.0 3.6.5-3.el10_0.15

red hat advisories RHSA-2026:19143RHSA-2026:17482RHSA-2026:15968

  • libsoup SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Basesystem 15 SP7 3.4.4-150600.3.47.1
  • libsoup SLES for SAP applications 16.0, SLES 16.0 3.6.6-160000.2.1

suse advisories SUSE-SU-2026:2314-1SUSE-SU-2026:21998-1

  • libsoup openSUSE Tumbleweed 3.6.6-5.1

opensuse advisories openSUSE-SU-2026:10911-1

  • libsoup3 AlmaLinux 10 3.6.5-3.el10_2.11

almalinux advisories ALSA-2026:19143

  • libsoup3 Rocky Linux 10 3.6.5-3.el10_1.11

rocky linux advisories RLSA-2026:15968

Is CVE-2026-4271 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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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-2026-4271 updated cvss 5.3

libsoup: libsoup: Denial of Service via Use-After-Free in HTTP/2 server

  • Red Hat Enterprise Linux 6 libsoup
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Enterprise Linux AppStream (v. 10) libsoup3 3.6.5-3.el10_1.11, libsoup3 3.6.5-3.el10_2.11
    fixed: vendor fix RHSA-2026:15968
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) libsoup3 3.6.5-3.el10_0.15
    fixed: vendor fix RHSA-2026:17482
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libsoup3-doc 3.6.5-3.el10_1.11, libsoup3-doc 3.6.5-3.el10_2.11
    fixed: vendor fix RHSA-2026:15968
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) libsoup3-doc 3.6.5-3.el10_0.15
    fixed: vendor fix RHSA-2026:17482
  • Red Hat Enterprise Linux 7 libsoup Red Hat Enterprise Linux 8 libsoup Red Hat Enterprise Linux 9 libsoup
    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
7mo ago

Exploit prediction

0.88% chance of exploitation in the next 30 days, higher than 59% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • gitlab.gnome.org https://gitlab.gnome.org/GNOME/libsoup/-/issues/496 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9

Classification

Weakness

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.