Medium [CVE-2026-72522] Denial of Service due to incorrect Unicode surrogate handling
This medium-severity Red Hat Linux advisory covers CVE-2026-72522 affecting Red Hat Hardened Images, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7.
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Summary
libexpat before 2.8.3 has an out-of-bounds read and resultant infinite loop because low surrogates are treated the same as high surrogates during Unicode processing in the *_toUtf16 functions. An attacker can exploit the resulting out-of-bounds read to trigger an infinite loop, causing a denial of service (DoS).
A denial of service (DoS) flaw was found in libexpat's handling of Unicode surrogate pairs. An attacker providing specially crafted XML input to an application parsing untrusted data can trigger an out-of-bounds read and an infinite loop, leading to high CPU usage and system resource exhaustion.
Red Hat severity: Moderate — CVSS 6.2 (CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-125.
Affected Red Hat products: Red Hat Hardened Images; Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9.
Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat OpenShift Container Platform 4 as not affected. Red Hat fixing advisory: RHSA-2026:54869.
Affected products named by the advisory: Red Hat package: firefox; Red Hat package: thunderbird; Red Hat package: mingw-expat.
- < 2.8.3
Official advisory · high-confidence parse· fetched 25 days ago·verify at source
- expat-main-2.8.3-0.1.hum1
- RHSA-2026:54869
Official advisory · high-confidence parse· fetched 25 days ago·verify at source
Mitigation checklist
- Limit exposure by restricting the parsing of untrusted or unverified XML inputs, and validate incoming XML documents for malformed character sequences before processing. Additionally, enforce process-level CPU resource limits and parsing timeouts to prevent system-wide Denial of Service from infinite parsing loops.
Official advisory · high-confidence parse· fetched 25 days ago·verify at source
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