CVE-2026-76641
Description
A flaw was found in Expat. Attackers can exploit an out-of-bounds read vulnerability by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. This can lead to memory corruption. Specifically, a mismatch in struct sizes can cause a read past memory boundaries, potentially resulting in a denial of service (DoS) due to a segfault or incorrect handling of XML attributes.
Statement
Important: An out-of-bounds read vulnerability in Expat can lead to memory corruption and denial of service when processing specially crafted XML with external entity parsers.
Mitigation
To mitigate this implement a strict "accept known good" input validation strategy that rejects any data failing to match expected specifications. Rigorously validate all length arguments, offsets, and buffer size calculations before using them to access memory boundaries. Additionally, avoid relying solely on sentinels (such as NUL characters) within untrusted input to determine array or buffer lengths. Finally, apply defense-in-depth by combining allowlists with denylists to aggressively drop outright malformed inputs before processing begins.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: 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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
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