CVE-2026-102633
Description
A flaw was found in expat. On 32-bit systems, an integer overflow occurs within the expat_realloc memory allocation function when calculating buffer sizes. A remote attacker can exploit this vulnerability by supplying specially crafted XML input to an application that processes data with the library. Successful exploitation can lead to a Denial of Service (DoS) or memory corruption.
Statement
A flaw of moderate impact was found in the expat XML parser library (libexpat), which is shipped in Red Hat Enterprise Linux and Fedora. On 32-bit systems, an integer overflow can occur in the expat_realloc() memory allocation function when buffer sizes are calculated, resulting in an undersized heap allocation that can lead to a heap buffer overflow, memory corruption, or a crash. A remote attacker can supply specially crafted XML input to an application that processes data with the vulnerable library, causing a denial of service of that application; no privileges or user interaction are required, but exploitation is limited to 32-bit platforms and requires triggering specific allocation sizes, so attack complexity is high.
Red Hat Product Security rates this flaw Moderate (CVSS 3.1 score 5.9, AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H), which differs from the upstream CVSS 4.0 rating of Important (8.2) because the vulnerability is restricted to 32-bit architectures with high attack complexity and its impact is limited to availability.
Affected expat and mingw-expat components span Red Hat Enterprise Linux 6 through 10, Red Hat In-Vehicle OS, Red Hat Hardened Images, and Fedora. For Red Hat Enterprise Linux and UBI-related streams, fixes are being pursued through delegated updates. For several maintenance streams the fix is deferred because the flaw is Moderate severity with a CVSS score below 7.0, leaving a residual risk of denial of service or memory corruption on 32-bit deployments until a fix is delivered. Red Hat Enterprise Linux 6 and certain platform streams are out of support scope and will not be fixed. The expat package in Red Hat Hardened Images (Hummingbird) is not affected because the vulnerable code is not present.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
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 | 5.9 | N/A | 5.9 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| 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:H/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; DoS: Resource Consumption (Memory); DoS: Instability
This weakness can generally lead to undefined behavior and therefore crashes. When the calculated result is used for resource allocation, this weakness can cause too many (or too few) resources to be allocated, possibly enabling crashes if the product requests more resources than can be provided. If the calculated result involves time values, then the product might crash when it encounters a time that is less than the previously-calculated time.
Integrity
Technical Impact: Modify Memory
If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the overflow/wraparound results in other conditions such as buffer overflows, further memory corruption may occur.
Confidentiality,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism
This weakness can sometimes trigger buffer overflows, which can be used to execute arbitrary code. This is usually outside the scope of the product's implicit security policy.
Availability,Other
Technical Impact: Alter Execution Logic; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
If the overflow/wraparound occurs in a loop index variable, this could cause the loop to terminate at the wrong time - too early, too late, or not at all (i.e., infinite loops). With too many iterations, some loops could consume too many resources such as memory, file handles, etc., possibly leading to a crash or other DoS.
Access Control
Technical Impact: Bypass Protection Mechanism
If integer values are used in security-critical decisions, such as calculating quotas or allocation limits, integer overflows can be used to cause an incorrect security decision.
Access Control
Technical Impact: Bypass Protection Mechanism; DoS: Crash, Exit, or Restart
If integer values are used in time-based, security-critical decisions, such as calculating expiration times or determining whether an event occurs within a specific time or date range, to cause an incorrect security decision. The consequences could even include "self-DoS" if the overflow produces a time value that is not accounted for in protection mechanism logic [REF-1570].
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