Description
Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| libexpat project | libexpat | ≤ 2.8.3 | — |
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 | 2.8.4-1 | — |
| 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 +5 | No fix yet | — |
| Ubuntu 26.04 LTS | expat | 2.7.4-1ubuntu0.2 | USN-8813-1 |
| Ubuntu 26.04 LTS | tdom +4 | No fix yet | — |
| Ubuntu 24.04 LTS | expat | 2.6.1-2ubuntu0.6 | USN-8813-1 |
| Ubuntu 24.04 LTS | tdom +3 | No fix yet | — |
| Ubuntu 22.04 LTS | expat | 2.4.7-1ubuntu0.9 | USN-8813-1 |
| Ubuntu 22.04 LTS | tdom +4 | 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 | tdom +6 | No fix yet | — |
| Ubuntu 16.04 LTS | tdom +5 | 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 | 2.2.9-1ubuntu0.8+esm3 | USN-8813-1 |
| Ubuntu Pro 20.04 LTS | swish-e +2 | No fix yet | — |
| Ubuntu Pro 18.04 LTS | coin3 +3 | No fix yet | — |
| Ubuntu Pro 18.04 LTS | expat | 2.2.5-3ubuntu0.9+esm5 | USN-8813-1 |
| Ubuntu Pro 16.04 LTS | expat | 2.1.0-7ubuntu0.16.04.5+esm14 | USN-8813-1 |
| Ubuntu Pro 16.04 LTS | vtk +7 | No fix yet | — |
| Ubuntu Pro 14.04 LTS | expat | 2.1.0-4ubuntu1.4+esm13 | USN-8813-1 |
| Ubuntu Pro 14.04 LTS | vtk +3 | No fix yet | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | expat +1 | 2.7.3-1.el10_2.5 | RHSA-2026:74001 |
| RHEL 9 | expat +1 | 2.5.0-6.el9_8.5 | 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 | 2.8.4-0.1.hum1 | RHSA-2026:65568 |
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-2026:74001 |
| Rocky Linux 9 | expat | 2.5.0-6.el9_8.5 | RLSA-2026:72663 |
| 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 | 2.8.4-160000.1.1 | SUSE-SU-2026:23912-1 |
| 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 | 2.8.4-160000.1.1 | SUSE-SU-2026:23912-1 |
| SLE Micro 6.2 | expat | 2.8.4-160000.1.1 | SUSE-SU-2026:23894-1 |
| 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 | 2.8.4-1.1 | openSUSE-SU-2026:11733-1 |
| openSUSE Leap 16.0 | MozillaFirefox | 153.5.0-160000.1.1 | openSUSE-SU-2026:22139-1 |
| openSUSE Leap 16.0 | expat | 2.8.4-160000.1.1 | openSUSE-SU-2026:21945-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | expat | 2.8.4-r0 | — |
| Alpine v3.23 | expat | 2.8.4-r0 | — |
| Alpine v3.22 | expat | 2.8.4-r0 | — |
| Alpine v3.21 | expat | 2.8.4-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | expat +2 | 2.8.3-1.amzn2023.0.1 | ALAS2023-2026-2157 |
| Amazon Linux 2023 | firefox | 140.14.0-1.amzn2023.0.1 | ALAS2023-2026-2105 |
| Amazon Linux 2 | expat +2 | 2.1.0-15.amzn2.0.9 | ALAS2-2026-3965 |
| Amazon Linux 2 | thunderbird | 140.14.0-1.amzn2.0.1 | ALAS2-2026-3880 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | expat | 2.8.3-2 | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 10 | expat +1 | 2.7.3-1.el10_2.5 | ELSA-2026-74001 |
| Oracle Linux 9 | expat +1 | 2.5.0-6.el9_8.5 | ELSA-2026-72663 |
| Oracle Linux 8 | expat +1 | 2.5.0-4.el8_10 | ELSA-2026-72448 |
Advisories 35
- WID-SEC-2026-2906 expat: Schwachstelle ermöglicht Denial of Service BSI CERT-Bund (WID) · Nov 11, 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
- SUSE-SU-2026:24554-1 Security update for expat SUSE / openSUSE Security Updates · Nov 7, 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-2026:65568 Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update Red Hat Security Advisories (RHSA) · Oct 17, 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
- WID-SEC-2026-3642 Meinberg LANTIME: Mehrere Schwachstellen BSI CERT-Bund (WID) · Oct 14, 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
- ALAS2-2026-3965 Important: expat security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Oct 12, 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
- SUSE-SU-2026:23912-1 Security update for expat SUSE / openSUSE Security Updates · Sep 30, 2026
- SUSE-SU-2026:23894-1 Security update for expat SUSE / openSUSE Security Updates · Sep 30, 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
- openSUSE-SU-2026:21945-1 Security update for expat SUSE / openSUSE Security Updates · Sep 25, 2026
- USN-8813-1 expat vulnerabilities Ubuntu Security Notices (USN) · Sep 25, 2026
- ALAS2023-2026-2157 Important: expat security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Sep 14, 2026
- openSUSE-SU-2026:11733-1 expat-2.8.4-1.1 on GA media SUSE / openSUSE Security Updates · Sep 10, 2026
- ALAS2-2026-3880 Important: thunderbird security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Aug 31, 2026
- ALAS2023-2026-2105 Important: firefox security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 31, 2026
References
- Pull Request issue-tracking patch
- https://www.vulncheck.com/advisories/expat-denial-of-service-via-storeatts-quadratic-complexity third-party-advisory