Description
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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| libexpat | libexpat | < 2.8.5 | 2.8.5 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | expat | 2.8.4-2 | — |
| Debian 13 | expat | 2.9.0-1~deb13u1 | — |
| Debian 12 | expat | 2.5.0-1+deb12u4 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | tdom +6 | No fix yet | — |
| Ubuntu 26.04 LTS | tdom +5 | No fix yet | — |
| Ubuntu 24.04 LTS | tdom +4 | No fix yet | — |
| Ubuntu 22.04 LTS | tdom +5 | No fix yet | — |
| Ubuntu 20.04 LTS | tdom +4 | No fix yet | — |
Show 9 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | gdcm +7 | No fix yet | — |
| Ubuntu 16.04 LTS | gdcm +6 | No fix yet | — |
| Ubuntu Pro 26.04 LTS | swish-e | No fix yet | — |
| Ubuntu Pro 24.04 LTS | swish-e +2 | No fix yet | — |
| Ubuntu Pro 22.04 LTS | swish-e +2 | No fix yet | — |
| Ubuntu Pro 20.04 LTS | expat +3 | No fix yet | — |
| Ubuntu Pro 18.04 LTS | coin3 +4 | No fix yet | — |
| Ubuntu Pro 16.04 LTS | vtk +8 | No fix yet | — |
| Ubuntu Pro 14.04 LTS | vtk +4 | No fix yet | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | expat +1 | 2.7.3-1.el10_2.5 | RHSA-2026:98582, RHSA-2026:74001 |
| RHEL 9 | expat +1 | 2.5.0-6.el9_8.5 | RHSA-2026:98478, RHSA-2026:72663 |
| RHEL 8 | expat +1 | 2.5.0-4.el8_10 | RHSA-2026:72448 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | expat +2 | 2.8.4-0.2.hum1 | RHSA-2026:71655 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 10 | expat +1 | 2.7.3-1.el10_2.5 | ALSA-2026:74001 |
| AlmaLinux 9 | expat +1 | 2.5.0-6.el9_8.5 | ALSA-2026:72663 |
| AlmaLinux 8 | expat +1 | 2.5.0-4.el8_10 | ALSA-2026:72448 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | expat | 2.7.3-1.el10_2.5 | RLSA-2026:98582, RLSA-2026:74001 |
| Rocky Linux 10 | expat-devel | 2.7.3-2.el10_3.4 | RLSA-2026:98582 |
| Rocky Linux 9 | expat | 2.5.0-6.el9_8.5 | RLSA-2026:98478, RLSA-2026:72663 |
| Rocky Linux 9 | expat-devel | 2.5.0-9.el9_9.4 | RLSA-2026:98478 |
| Rocky Linux 8 | expat | 2.5.0-4.el8_10 | RLSA-2026:72448 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLES 15 SP7 | MozillaThunderbird | 153.5.0-150400.13.9.1 | SUSE-SU-2026:4736-1 |
| SLES 15 SP7 | expat | 2.8.5-150700.3.15.1 | SUSE-SU-2026:4619-1 |
| SLES 15 SP6 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLES 15 SP6 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLES 15 SP5 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLES 15 SP5 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLES 15 SP4 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLES 15 SP4 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLES 12 SP5 | MozillaFirefox | 153.5.0-118.16.2 | SUSE-SU-2026:4806-1 |
| SLES 12 SP5 | expat | 2.8.5-21.55.1 | SUSE-SU-2026:4615-1 |
Show 13 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | MozillaFirefox | 153.5.0-160000.1.1 | SUSE-SU-2026:24260-1 |
| SLES for SAP 16.0 | expat | 2.8.5-160000.1.1 | SUSE-SU-2026:24469-1 |
| SLES for SAP 15 SP6 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLES for SAP 15 SP6 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLES for SAP 15 SP5 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLES for SAP 15 SP5 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLES for SAP 15 SP4 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLES for SAP 15 SP4 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLES 16.0 | MozillaFirefox | 153.5.0-160000.1.1 | SUSE-SU-2026:24260-1 |
| SLES 16.0 | expat | 2.8.5-160000.1.1 | SUSE-SU-2026:24469-1 |
| SLE Micro 6.2 | expat | 2.8.5-160000.1.1 | SUSE-SU-2026:24460-1 |
| SLE Micro 6.1 | expat | 2.8.5-slfo.1.1_1.1 | SUSE-SU-2026:24554-1 |
| SLE Micro 6.0 | expat | 2.8.5-159998.1.1 | SUSE-SU-2026:24323-1 |
| SLE Micro 5.5 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLE Micro 5.4 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLE Micro 5.3 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLE HPC 15 SP5 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLE HPC 15 SP5 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
| SLE HPC 15 SP4 | MozillaFirefox | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 |
| SLE HPC 15 SP4 | expat | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | expat | 2.8.5-1.1 | openSUSE-SU-2026:11981-1 |
| openSUSE Leap 16.0 | MozillaFirefox | 153.5.0-160000.1.1 | openSUSE-SU-2026:22139-1 |
| openSUSE Leap 16.0 | expat | 2.8.5-160000.1.1 | openSUSE-SU-2026:22177-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | expat | 2.8.5-r0 | — |
| Alpine v3.23 | expat | 2.8.5-r0 | — |
| Alpine v3.22 | expat | 2.8.5-r0 | — |
| Alpine v3.21 | expat | 2.8.5-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | firefox | 140.17.0-1.amzn2023.0.1 | ALAS2023-2026-3214 |
| Amazon Linux 2 | thunderbird | 153.5.1-1.amzn2.0.1 | ALAS2-2026-4057 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | expat | 2.8.5-1 | — |
| Azure Linux 3 | ogdi +2 | No fix yet | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 10 | expat +1 | 2.7.3-1.el10_2.5 | ELSA-2026-74001 |
| Oracle Linux 10 | thunderbird | 153.6.0-1.0.1.el10_2 | ELSA-2026-96079 |
| Oracle Linux 9 | expat +1 | 2.5.0-6.el9_8.5 | ELSA-2026-72663 |
| Oracle Linux 9 | thunderbird | 153.6.0-1.0.1.el9_8 | ELSA-2026-96081 |
| Oracle Linux 8 | expat +1 | 2.5.0-4.el8_10 | ELSA-2026-72448 |
Advisories 37
- RHSA-2026:98478 Red Hat Security Advisory: expat security update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:98582 Red Hat Security Advisory: expat security update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RLSA-2026:98582 Important: expat security update Rocky Linux Security Advisories · Nov 13, 2026
- RLSA-2026:98478 Important: expat security update Rocky Linux Security Advisories · Nov 13, 2026
- WID-SEC-2026-3482 expat: Schwachstelle ermöglicht Manipulation von Daten BSI CERT-Bund (WID) · Nov 12, 2026
- SSA-457936 SSA-457936: Vulnerabilities in the additional GNU/Linux subsystem of the SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP V3.1.7 Siemens ProductCERT · Nov 10, 2026
- ELSA-2026-96079 Important: thunderbird security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Nov 9, 2026
- ELSA-2026-96081 Important: thunderbird security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Nov 9, 2026
- SUSE-SU-2026:24554-1 Security update for expat SUSE / openSUSE Security Updates · Nov 7, 2026
- SUSE-SU-2026:24469-1 Security update for expat SUSE / openSUSE Security Updates · Nov 4, 2026
- SUSE-SU-2026:24460-1 Security update for expat SUSE / openSUSE Security Updates · Nov 2, 2026
- ALAS2-2026-4057 Important: thunderbird security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Nov 2, 2026
- openSUSE-SU-2026:22177-1 Security update for expat SUSE / openSUSE Security Updates · Nov 1, 2026
- ALAS2023-2026-3214 Important: firefox security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Oct 29, 2026
- ALSA-2026:72663 Important: expat security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:74001 Important: expat security update AlmaLinux Security Advisories · Oct 29, 2026
- ALSA-2026:72448 Important: expat security update AlmaLinux Security Advisories · Oct 29, 2026
- SUSE-SU-2026:24323-1 Security update for expat SUSE / openSUSE Security Updates · Oct 27, 2026
- SUSE-SU-2026:24260-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Oct 23, 2026
- openSUSE-SU-2026:22139-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Oct 22, 2026
- SUSE-SU-2026:4834-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Oct 22, 2026
- SUSE-SU-2026:4806-1 Security update for MozillaFirefox SUSE / openSUSE Security Updates · Oct 21, 2026
- SUSE-SU-2026:4736-1 Security update for MozillaThunderbird SUSE / openSUSE Security Updates · Oct 20, 2026
- SUSE-SU-2026:4619-1 Security update for expat SUSE / openSUSE Security Updates · Oct 19, 2026
- RHSA-2026:74001 Red Hat Security Advisory: expat security update Red Hat Security Advisories (RHSA) · Oct 15, 2026
- RHSA-2026:72663 Red Hat Security Advisory: expat security update Red Hat Security Advisories (RHSA) · Oct 15, 2026
- RHSA-2026:72448 Red Hat Security Advisory: expat security update Red Hat Security Advisories (RHSA) · Oct 15, 2026
- RHSA-2026:71655 Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update Red Hat Security Advisories (RHSA) · Oct 15, 2026
- SUSE-SU-2026:4623-1 Security update for expat SUSE / openSUSE Security Updates · Oct 13, 2026
- SUSE-SU-2026:4615-1 Security update for expat SUSE / openSUSE Security Updates · Oct 13, 2026
- openSUSE-SU-2026:11981-1 expat-2.8.5-1.1 on GA media SUSE / openSUSE Security Updates · Oct 5, 2026
- RLSA-2026:74001 Important: expat security update Rocky Linux Security Advisories · Oct 1, 2026
- ELSA-2026-74001 Important: expat security update (Oracle Linux 10) Oracle Linux Security Advisories (ELSA) · Oct 1, 2026
- RLSA-2026:72663 Important: expat security update Rocky Linux Security Advisories · Sep 30, 2026
- RLSA-2026:72448 Important: expat security update Rocky Linux Security Advisories · Sep 29, 2026
- ELSA-2026-72448 Important: expat security update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Sep 29, 2026
- ELSA-2026-72663 Important: expat security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Sep 28, 2026
References
- GitHub PR #1282 issue-tracking patch
- https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a patch
- libexpat R_2_8_5 Release Notes release-notes
- https://blog.hartwork.org/posts/expat-2-8-5-released/ vendor-advisory
- https://github.com/libexpat/libexpat product
- VulnCheck Advisory: Expat through 2.8.4 Malformed UTF-16 Acceptance via Unchecked Surrogate third-party-advisory