CVE-2026-117610
Description
A flaw was found in expat. A remote attacker who controls input stream chunking can trigger a NULL pointer dereference by forcing an empty initial parse on an external entity subparser. Successful exploitation causes the application to crash, resulting in a Denial of Service (DoS).
Statement
This vulnerability is rated Moderate. Confirmed impact is denial of service (NULL dereference / crash) when an empty non-final first parse is performed on an external-entity subparser. Red Hat scores CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H (5.9): Attack Complexity is High because exploitation needs uncommon stream-chunking behavior together with external entity parsing, which is not the default posture for most RHEL XML consumers. Hardening (ASLR/NX/FORTIFY/SELinux) does not prevent the crash DoS; Availability remains High. No confidentiality or integrity impact is demonstrated.
Mitigation
Avoid enabling external entity / DTD processing for untrusted XML; prefer parsers configured without external entity resolution. Do not expose stream-chunked XML parse APIs to untrusted clients. Restrict network access to XML-processing services ([CME-202](https://cmetaxonomy.org/entries/CME-202.html), [CME-203](https://cmetaxonomy.org/entries/CME-203.html)). Upgrade to libexpat 2.10.0 or later when available.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 7.5 | 5.9 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | Low | High |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | None | None | None |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
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