CVE-2026-118370
Received Received - Intake

Integer Overflow in Expat XML Parser Leading to Heap Corruption

Publication date: 2026-10-28

Last updated on: 2026-10-28

Assigner: VulnCheck

Description
libexpat through 2.9.0 contains a signed integer overflow vulnerability in storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds writes via oversized attribute counts. Attackers can supply a multi-gigabyte document with a start tag carrying over 2^30 attributes to overflow attIndex and nPrefixes, crashing applications or corrupting heap memory.

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Meta Information

Published
2026-10-28
Last Modified
2026-10-28
Generated
2026-10-28
AI Q&A
2026-10-28
EPSS Evaluated
N/A
NVD
CVE-2026-118370
EUVD
EUVD-2026-111546

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
libexpat libexpat 0

Helpful Resources

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

This vulnerability is a signed integer overflow in libexpat through version 2.9.0. It occurs in the storeAtts() function in lib/xmlparse.c when processing XML documents with an excessive number of attributes. Attackers can exploit this by providing a document with a start tag containing over 2^30 attributes, causing overflows in attIndex and nPrefixes variables. This leads to out-of-bounds writes, potentially crashing applications or corrupting heap memory.

Detection Guidance

To detect this vulnerability, monitor for crashes or memory corruption in applications using libexpat versions 2.9.0 or earlier when processing large XML files. Check for logs indicating out-of-bounds writes or heap corruption during XML parsing.

Impact Analysis

This vulnerability can impact you by causing applications using libexpat to crash or behave unpredictably. It may also lead to memory corruption, which could be exploited for further attacks like code execution. Systems processing untrusted XML input are particularly at risk.

Mitigation Strategies
  • Upgrade libexpat to a patched version (2.10.0 or later) where the integer overflow issue is fixed.
  • Apply the specific commits addressing the issue (e.g., 1bac53c, 621cb2c) or merge PR #1450.
  • Restrict processing of untrusted XML files or implement size limits for XML attributes.

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