HIGH

CVE-2026-66046

CVSS v3

7.5

HIGH

EPSS Score

0.7 %

exploit probability, as of 2026-10-18

CISA KEV

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

expatAlmaLinux:10all versions · fixed in 2.7.3-1.el10_2.5and 1 other package
expatAlmaLinux:9all versions · fixed in 2.5.0-6.el9_8.5and 1 other package
expatAlmaLinux:8all versions · fixed in 2.5.0-4.el8_10and 1 other package

Vendor advisories

CVE-2026-66046 Red Hat Product Security90 products fixed · 35 known affected
expat: Expat: Denial of Service via quadratic complexity in attribute processing
firefox as a component of Red Hat Enterprise Linux 10 · firefox.src as a component of Red Hat Enterprise Linux 10 · thunderbird as a component of Red Hat Enterprise Linux 10
RHSA-2026:82939 Red Hat Product Security5 products fixed
Red Hat Security Advisory: Red Hat Update Infrastructure 5.3 security update
RHSA-2026:79357 Red Hat Product Security1 product fixed
Red Hat Security Advisory: Red Hat Cost Management On-Premise container image update
RHSA-2026:74001 Red Hat Product Security25 products fixed
Red Hat Security Advisory: expat security update
RHSA-2026:72663 Red Hat Product Security31 products fixed
Red Hat Security Advisory: expat security update
RHSA-2026:72448 Red Hat Product Security21 products fixed
Red Hat Security Advisory: expat security update

1 more advisory

Full record on NVD

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.

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2026-08-18
Last Modified: 2026-08-18

Frequently asked questions

What is CVE-2026-66046?

Is CVE-2026-66046 actively exploited?

Active exploitation of CVE-2026-66046 has not been confirmed. Its EPSS score was 0.7% on 2026-10-18, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-66046?

CVE-2026-66046 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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