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Fencer Vulns
medium 6.9

CVE-2026-86143 json

In xmlIO in libxml2 before 2.15.4, an inconsistency in xmlOutputWriteCallback and xmlBufUse causes negative lengths to reach write callback…

published 2026-09-05 2 mo ago modified 2026-09-15 54 d ago also EUVD-2026-71822

cvss
6.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits
0
none known

Summary

In xmlIO in libxml2 before 2.15.4, an inconsistency in xmlOutputWriteCallback and xmlBufUse causes negative lengths to reach write callbacks, aka a lack of a check for integer overflow before calling writecallback. This has security relevance for many types of uses of that length value within a callback.

Patch / fix

  • xmlsoft libxml2 2.15.4
  • libxml2 Debian 14 2.15.4+dfsg-1

debian advisories DEBIAN-CVE-2026-86143

  • libxml2 Ubuntu 22.04 LTS 2.9.13+dfsg-1ubuntu0.14
  • libxml2 Ubuntu 24.04 LTS 2.9.14+dfsg-1.3ubuntu3.10
  • libxml2 Ubuntu 26.04 LTS 2.15.2+dfsg-0.1ubuntu0.3
  • libxml2 Ubuntu Pro 14.04 LTS 2.9.1+dfsg1-3ubuntu4.13+esm13
  • libxml2 Ubuntu Pro 16.04 LTS 2.9.3+dfsg1-1ubuntu0.7+esm14
  • libxml2 Ubuntu Pro 18.04 LTS 2.9.4+dfsg1-6.1ubuntu1.9+esm9
  • libxml2 Ubuntu Pro 20.04 LTS 2.9.10+dfsg-5ubuntu0.20.04.10+esm6

ubuntu advisories UBUNTU-CVE-2026-86143

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

  • libxml2 RHEL 8 2.9.7-21.el8_10.9
  • python3-libxml2 RHEL 8 2.9.7-21.el8_10.9
  • libxml2 RHEL 10.2 2.12.5-10.el10_2.4
  • python3-libxml2 RHEL 10.2 2.12.5-10.el10_2.4
  • libxml2 RHEL 9 2.9.13-14.el9_8.5
  • python3-libxml2 RHEL 9 2.9.13-14.el9_8.5
  • libxml2 hummingbird 1 2.15.4-0.1.hum1
  • libxml2-16 hummingbird 1 2.15.4-0.1.hum1

red hat advisories RHSA-2026:71641RHSA-2026:71586RHSA-2026:71585RHSA-2026:64463

  • libxml2 AlmaLinux 9 2.9.13-14.el9_8.5
  • python3-libxml2 AlmaLinux 9 2.9.13-14.el9_8.5
  • libxml2 AlmaLinux 10 2.12.5-10.el10_2.4
  • python3-libxml2 AlmaLinux 10 2.12.5-10.el10_2.4
  • libxml2 AlmaLinux 8 2.9.7-21.el8_10.9
  • python3-libxml2 AlmaLinux 8 2.9.7-21.el8_10.9

almalinux advisories ALSA-2026:71585ALSA-2026:71586ALSA-2026:71641

  • libxml2 Rocky Linux 8 2.9.7-21.el8_10.9
  • libxml2 Rocky Linux 9 2.9.13-14.el9_8.5
  • libxml2 Rocky Linux 10 2.12.5-10.el10_2.4

rocky linux advisories RLSA-2026:71641RLSA-2026:71585RLSA-2026:71586

  • libxml2 Azure Linux 3.0 2.11.5-11

azure linux advisories AZL-99705

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-2026-86143 updated cvss 6.9

libxml2: libxml2: Data integrity issues due to integer overflow in write callbacks

  • Red Hat Enterprise Linux 6 libxml2, libxml2-python
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/cert-manager-operator-rhel9 1790589855, cert-manager/jetstack-cert-manager-rhel9 1790589912, cert-manager/cert-manager-istio-csr-rhel9 1790589914
    fixed: vendor fix RHSA-2026:72475
  • Red Hat Cost Management On-Premise 1 costmanagement/costmanagement-ui-rhel10 1791460851
    fixed: vendor fix RHSA-2026:79357
  • Red Hat Enterprise Linux AppStream (v. 8) libxml2-devel 2.9.7-21.el8_10.9, libxml2-debuginfo 2.9.7-21.el8_10.9, libxml2-debugsource 2.9.7-21.el8_10.9, python3-libxml2-debuginfo 2.9.7-21.el8_10.9
    fixed: vendor fix RHSA-2026:71641
  • Red Hat Enterprise Linux AppStream (v. 9) libxml2-devel 2.9.13-14.el9_8.5, libxml2-debuginfo 2.9.13-14.el9_8.5, libxml2-debugsource 2.9.13-14.el9_8.5, python3-libxml2-debuginfo 2.9.13-14.el9_8.5
    fixed: vendor fix RHSA-2026:71585
  • Red Hat Enterprise Linux AppStream (v. 10) libxml2-devel 2.12.5-10.el10_2.4, libxml2-debuginfo 2.12.5-10.el10_2.4, libxml2-debugsource 2.12.5-10.el10_2.4, python3-libxml2-debuginfo 2.12.5-10.el10_2.4
    fixed: vendor fix RHSA-2026:71586
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) libxml2-devel 2.9.7-9.el8_4.20, libxml2-debuginfo 2.9.7-9.el8_4.20, libxml2-debugsource 2.9.7-9.el8_4.20, python3-libxml2-debuginfo 2.9.7-9.el8_4.20
    fixed: vendor fix RHSA-2026:93473
show 30 more
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) libxml2-devel 2.9.7-13.el8_6.24, libxml2-debuginfo 2.9.7-13.el8_6.24, libxml2-debugsource 2.9.7-13.el8_6.24, python3-libxml2-debuginfo 2.9.7-13.el8_6.24
    fixed: vendor fix RHSA-2026:92589
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) libxml2-devel 2.9.7-16.el8_8.24, libxml2-debuginfo 2.9.7-16.el8_8.24, libxml2-debugsource 2.9.7-16.el8_8.24, python3-libxml2-debuginfo 2.9.7-16.el8_8.24
    fixed: vendor fix RHSA-2026:93463
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) libxml2-devel 2.9.13-3.el9_2.20, libxml2-debuginfo 2.9.13-3.el9_2.20, libxml2-debugsource 2.9.13-3.el9_2.20, python3-libxml2-debuginfo 2.9.13-3.el9_2.20
    fixed: vendor fix RHSA-2026:92352
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) libxml2-devel 2.9.13-13.el9_4.10, libxml2-debuginfo 2.9.13-13.el9_4.10, libxml2-debugsource 2.9.13-13.el9_4.10, python3-libxml2-debuginfo 2.9.13-13.el9_4.10
    fixed: vendor fix RHSA-2026:89750
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) libxml2-devel 2.12.5-9.el10_0.9, libxml2-debuginfo 2.12.5-9.el10_0.9, libxml2-debugsource 2.12.5-9.el10_0.9, python3-libxml2-debuginfo 2.12.5-9.el10_0.9
    fixed: vendor fix RHSA-2026:89759
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) libxml2-devel 2.9.13-13.el9_6, libxml2-debuginfo 2.9.13-13.el9_6, libxml2-debugsource 2.9.13-13.el9_6, python3-libxml2-debuginfo 2.9.13-13.el9_6
    fixed: vendor fix RHSA-2026:90309
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) libxml2-devel 2.9.7-9.el8_4.20, libxml2-debuginfo 2.9.7-9.el8_4.20, libxml2-debugsource 2.9.7-9.el8_4.20, python3-libxml2-debuginfo 2.9.7-9.el8_4.20
    fixed: vendor fix RHSA-2026:93473
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) libxml2-devel 2.9.7-13.el8_6.24, libxml2-debuginfo 2.9.7-13.el8_6.24, libxml2-debugsource 2.9.7-13.el8_6.24, python3-libxml2-debuginfo 2.9.7-13.el8_6.24
    fixed: vendor fix RHSA-2026:92589
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) libxml2-devel 2.9.7-16.el8_8.24, libxml2-debuginfo 2.9.7-16.el8_8.24, libxml2-debugsource 2.9.7-16.el8_8.24, python3-libxml2-debuginfo 2.9.7-16.el8_8.24
    fixed: vendor fix RHSA-2026:93463
  • Red Hat Enterprise Linux BaseOS (v. 8) libxml2 2.9.7-21.el8_10.9, python3-libxml2 2.9.7-21.el8_10.9
    fixed: vendor fix RHSA-2026:71641
  • Red Hat Enterprise Linux BaseOS (v. 9) libxml2 2.9.13-14.el9_8.5, python3-libxml2 2.9.13-14.el9_8.5
    fixed: vendor fix RHSA-2026:71585
  • Red Hat Enterprise Linux BaseOS (v. 10) libxml2 2.12.5-10.el10_2.4, python3-libxml2 2.12.5-10.el10_2.4
    fixed: vendor fix RHSA-2026:71586
  • Red Hat Enterprise Linux BaseOS AUS (v.8.4) libxml2 2.9.7-9.el8_4.20, python3-libxml2 2.9.7-9.el8_4.20
    fixed: vendor fix RHSA-2026:93473
  • Red Hat Enterprise Linux BaseOS AUS (v.8.6) libxml2 2.9.7-13.el8_6.24, python3-libxml2 2.9.7-13.el8_6.24
    fixed: vendor fix RHSA-2026:92589
  • Red Hat Enterprise Linux BaseOS E4S (v.8.8) libxml2 2.9.7-16.el8_8.24, python3-libxml2 2.9.7-16.el8_8.24
    fixed: vendor fix RHSA-2026:93463
  • Red Hat Enterprise Linux BaseOS E4S (v.9.2) libxml2 2.9.13-3.el9_2.20, python3-libxml2 2.9.13-3.el9_2.20
    fixed: vendor fix RHSA-2026:92352
  • Red Hat Enterprise Linux BaseOS E4S (v.9.4) libxml2 2.9.13-13.el9_4.10, python3-libxml2 2.9.13-13.el9_4.10
    fixed: vendor fix RHSA-2026:89750
  • Red Hat Enterprise Linux BaseOS EUS (v. 10.0) libxml2 2.12.5-9.el10_0.9, python3-libxml2 2.12.5-9.el10_0.9
    fixed: vendor fix RHSA-2026:89759
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) libxml2 2.9.13-13.el9_6, python3-libxml2 2.9.13-13.el9_6
    fixed: vendor fix RHSA-2026:90309
  • Red Hat Enterprise Linux BaseOS EUS EXTENSION (v.8.4) libxml2 2.9.7-9.el8_4.20, python3-libxml2 2.9.7-9.el8_4.20
    fixed: vendor fix RHSA-2026:93473
  • Red Hat Enterprise Linux BaseOS EUS EXTENSION (v.8.6) libxml2 2.9.7-13.el8_6.24, python3-libxml2 2.9.7-13.el8_6.24
    fixed: vendor fix RHSA-2026:92589
  • Red Hat Enterprise Linux BaseOS TUS (v.8.8) libxml2 2.9.7-16.el8_8.24, python3-libxml2 2.9.7-16.el8_8.24
    fixed: vendor fix RHSA-2026:93463
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libxml2-static 2.12.5-10.el10_2.4, libxml2-debuginfo 2.12.5-10.el10_2.4, libxml2-debugsource 2.12.5-10.el10_2.4, python3-libxml2-debuginfo 2.12.5-10.el10_2.4
    fixed: vendor fix RHSA-2026:71586
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) libxml2-static 2.12.5-9.el10_0.9, libxml2-debuginfo 2.12.5-9.el10_0.9, libxml2-debugsource 2.12.5-9.el10_0.9, python3-libxml2-debuginfo 2.12.5-9.el10_0.9
    fixed: vendor fix RHSA-2026:89759
  • Red Hat Enterprise Linux Server (v. 7 ELS) libxml2 2.9.1-6.el7_9.20, libxml2-python 2.9.1-6.el7_9.20 Red Hat Enterprise Linux Server Optional (v. 7 ELS) libxml2-static 2.9.1-6.el7_9.20, libxml2-debuginfo 2.9.1-6.el7_9.20
    fixed: vendor fix RHSA-2026:93791
  • Red Hat Hardened Images libxml2 2.15.4-0.1.hum1, libxml2-16 2.15.4-0.1.hum1, python3-libxml2 2.15.4-0.1.hum1
    fixed: vendor fix RHSA-2026:64463
  • Red Hat OpenShift AI 3.0 rhai/base-image-cpu-rhel9 1793042072, rhai/base-image-cpu-rhel9 1793329709, rhai/base-image-tpu-rhel9 1793041987, rhai/base-image-cuda-rhel9 1793042067, rhai/base-image-cuda-rhel9 1793328358, rhai/base-image-rocm-rhel9 1793041981, +1 more
    fixed: vendor fix RHSA-2026:94459
  • Red Hat OpenShift AI 3.4 rhai/base-image-cpu-rhel9 1793042088, rhai/base-image-tpu-rhel9 1793042006, rhai/base-image-gaudi-rhel9 1793042011, rhai/base-image-spyre-rhel9 1793042074, rhai/base-image-neuron-rhel9 1793042008, rhai/base-image-rocm-6.4-rhel9 1793041995, +4 more
    fixed: vendor fix RHSA-2026:91241
  • Red Hat OpenShift AI 3.5 rhai/base-image-cpu-rhel9 1793042162, rhai/base-image-tpu-rhel9 1793042010, rhai/base-image-gaudi-rhel9 1793042004, rhai/base-image-rubin-rhel9 1793042092, rhai/base-image-spyre-rhel9 1793042114, rhai/base-image-neuron-rhel9 1793042008, +4 more
    fixed: vendor fix RHSA-2026:91204
  • Red Hat OpenShift Container Platform 4.22 rhcos 4.22.9.8.202610241758
    fixed: vendor fix RHSA-2026:89197

1 more fixed, 7 more not affected in the full advisory

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
no
Technical impact
total
Assessed
2 mo ago

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • gitlab.gnome.org https://gitlab.gnome.org/GNOME/libxml2/-/work_items/1111 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.9 CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
NVD 3.1 7.3 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:L

Affected products

  • xmlsoft libxml2

Classification

Weakness

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.