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Fencer Intel
high 7.5

CVE-2026-93990 json

Expat before 2.8.5 Malformed UTF-16 Acceptance via Unchecked Surrogate

published last mo. modified yesterday also EUVD-2026-83618

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 35%
public exploits
0
none known

Summary

Expat before 2.8.5 fails to validate that a high surrogate in UTF-16 input is followed by a low surrogate, allowing malformed UTF-16 sequences to be accepted. Attackers can supply UTF-16 encoded XML containing lone high surrogates that consume the following code unit, causing Expat to pass unpaired surrogates to applications built with XML_UNICODE and to silently replace input characters in other builds.

Patch / fix

  • libexpat libexpat 2.8.5
  • expat Debian 12 2.5.0-1+deb12u4
  • expat Debian 13 2.9.0-1~deb13u1
  • expat Debian 14 2.8.4-2

debian advisories DEBIAN-CVE-2026-93990

  • expat RHEL 10.2 2.7.3-1.el10_2.5
  • expat RHEL 9 2.5.0-6.el9_8.5
  • expat RHEL 8 2.5.0-4.el8_10
  • expat hummingbird 1 2.8.4-0.2.hum1

red hat advisories RHSA-2026:74001RHSA-2026:72663RHSA-2026:72448RHSA-2026:71655

  • expat SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 2.8.5-160000.1.1
  • expat Linux Micro 6.1 2.8.5-slfo.1.1_1.1
  • MozillaFirefox SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 153.5.0-150400.157.16.1
  • MozillaFirefox SLES for SAP applications 16.0, SLES 16.0 153.5.0-160000.1.1
  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 153.5.0-150400.13.9.1
  • expat SLE Module for Basesystem 15 SP7 2.8.5-150700.3.15.1
  • expat Linux Micro 6.0 2.8.5-159998.1.1
  • expat SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +10 more 2.8.5-150400.3.40.1

suse advisories SUSE-SU-2026:24460-1SUSE-SU-2026:24469-1SUSE-SU-2026:24554-1SUSE-SU-2026:4834-1SUSE-SU-2026:4806-1SUSE-SU-2026:24260-1

  • expat openSUSE Leap 16.0 2.8.5-160000.1.1
  • MozillaFirefox openSUSE Leap 16.0 153.5.0-160000.1.1
  • expat openSUSE Tumbleweed 2.8.5-1.1

opensuse advisories openSUSE-SU-2026:22177-1openSUSE-SU-2026:22139-1openSUSE-SU-2026:11981-1

  • expat AlmaLinux 10 2.7.3-1.el10_2.5
  • expat AlmaLinux 8 2.5.0-4.el8_10
  • expat AlmaLinux 9 2.5.0-6.el9_8.5

almalinux advisories ALSA-2026:74001ALSA-2026:72448ALSA-2026:72663

  • expat Rocky Linux 10 2.7.3-1.el10_2.5
  • expat Rocky Linux 9 2.5.0-6.el9_8.5
  • expat Rocky Linux 8 2.5.0-4.el8_10

rocky linux advisories RLSA-2026:74001RLSA-2026:72663RLSA-2026:72448

  • expat Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 2.8.5-r0

alpine advisories ALPINE-CVE-2026-93990

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • expat Azure Linux 3.0 2.8.5-1

azure linux advisories AZL-103316

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

Is CVE-2026-93990 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.

Check with Fencer

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-2026-93990 updated cvss 7.5

expat: Expat: XML Injection via Malformed UTF-16 Input

  • Red Hat Enterprise Linux 6 expat, compat-expat1
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 expat, firefox Red Hat Enterprise Linux 8 firefox, xmlrpc-c, mingw-expat, thunderbird, xmlrpc-c-c++, mingw32-expat, +3 more Red Hat Enterprise Linux 9 firefox, firefox-x11, thunderbird Red Hat Enterprise Linux 10 firefox, thunderbird 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 Cost Management On-Premise 1 costmanagement/costmanagement-ui-rhel10 1791460851
    fixed: vendor fix RHSA-2026:79357
  • Red Hat Enterprise Linux AppStream (v. 9) expat-devel 2.5.0-6.el9_8.5, expat-devel 2.5.0-9.el9_9.4, expat-debuginfo 2.5.0-6.el9_8.5, expat-debuginfo 2.5.0-9.el9_9.4, expat-debugsource 2.5.0-6.el9_8.5, expat-debugsource 2.5.0-9.el9_9.4
    fixed: vendor fix RHSA-2026:72663
  • Red Hat Enterprise Linux AppStream (v. 10) expat-devel 2.7.3-1.el10_2.5, expat-devel 2.7.3-2.el10_3.4, expat-debuginfo 2.7.3-1.el10_2.5, expat-debuginfo 2.7.3-2.el10_3.4, expat-debugsource 2.7.3-1.el10_2.5, expat-debugsource 2.7.3-2.el10_3.4
    fixed: vendor fix RHSA-2026:74001
  • Red Hat Enterprise Linux BaseOS (v. 8) expat 2.5.0-4.el8_10
    fixed: vendor fix RHSA-2026:72448
  • Red Hat Enterprise Linux BaseOS (v. 9) expat 2.5.0-6.el9_8.5, expat 2.5.0-9.el9_9.4
    fixed: vendor fix RHSA-2026:72663
  • Red Hat Enterprise Linux BaseOS (v. 10) expat 2.7.3-1.el10_2.5, expat 2.7.3-2.el10_3.4
    fixed: vendor fix RHSA-2026:74001
show 3 more
  • Red Hat Hardened Images expat 2.8.4-0.2.hum1
    fixed: vendor fix RHSA-2026:71655
  • Red Hat OpenShift Container Platform 4.22 rhcos 4.22.9.8.202610241758
    fixed: vendor fix RHSA-2026:89197
  • Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1791978528, rhui5/rhua-rhel9 1791978693, rhui5/haproxy-rhel9 1791978528, rhui5/installer-rhel9 1791964013, rhui5/cds-kubernetes-rhel9 1791978534
    fixed: vendor fix RHSA-2026:82939

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
last mo.

Exploit prediction

0.41% chance of exploitation in the next 30 days, higher than 35% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 4.0 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CNA 4.0 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/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

  • libexpat libexpat
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0)
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0)
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0)
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)

Classification

Weakness
  • CWE-176 Improper Handling of Unicode Encoding

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.