CVE-2026-118370: libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes

Vulnerability summary

CVE-2026-118370 is a high (CVSS 8.2) Integer Overflow or Wraparound vulnerability in libexpat_project libexpat. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 33.2% of scored vulnerabilities.

Timeline

1. 28-10-2026
   PublishedVulnerability first disclosed.
2. 02-11-2026
   Last modifiedVulnerability information updated.

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.

• CWE-190Integer Overflow or WraparoundThe 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.