CVE-2026-56407
Received Received - Intake
Integer Overflow in Expat XML Parser

Publication date: 2026-06-21

Last updated on: 2026-06-21

Assigner: MITRE

Description
libexpat before 2.8.2 has an integer overflow in doProlog that is related to storeEntityValue and entity textLen.
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Meta Information
Published
2026-06-21
Last Modified
2026-06-21
Generated
2026-06-21
AI Q&A
2026-06-21
EPSS Evaluated
N/A
NVD
CVE-2026-56407
EUVD
EUVD-2026-38184
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
libexpat libexpat to 2.8.2 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-190 The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
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Executive Summary

The CVE-2026-56407 vulnerability is a signed integer overflow in the libexpat library, specifically in the handling of entity text lengths within the function storeEntityValue.

When the length of an entity value pool exceeds the maximum value for an integer (INT_MAX), the length value truncates to a negative integer. This causes a pointer calculation to produce an invalid memory address that precedes the intended buffer.

As a result, when the entity is referenced, the code may read or write outside the allocated buffer, potentially causing memory corruption or crashes.

The issue was fixed by capping the length before casting to an integer, preventing the overflow.

Impact Analysis

This vulnerability can lead to memory corruption or application crashes when processing XML entities with libexpat.

An attacker might exploit this flaw to cause denial of service by crashing the application or potentially execute arbitrary code if the memory corruption is leveraged.

Mitigation Strategies

To mitigate the CVE-2026-56407 vulnerability, you should update the libexpat library to version 2.8.2 or later, where the integer overflow issue in the storeEntityValue function has been fixed.

The fix caps the entity text length before casting to an integer, preventing the overflow and potential memory corruption or crashes.

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