Medium severity · published Oct 28, 2026
CVE-2026-118370
libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes
New
5.9
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 38% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
LI
libexpat · libexpat
through 2.9.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-118370
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-118370
patch
https://github.com/libexpat/libexpat/pull/1450
patch
https://github.com/libexpat/libexpat/commit/1bac53c4fc460a03cd9860f39501c7979f6750ae
patch
https://github.com/libexpat/libexpat/commit/621cb2c78b253ee023a86bc91d6ddb048481c04c
technical-description
https://github.com/libexpat/libexpat/blob/a76b1174c1ea52abb639a4c69d52b630a8a106a2/expat/lib/xmlparse.c#L4138-L4140
product
https://github.com/libexpat/libexpat
third-party-advisory
https://www.vulncheck.com/advisories/libexpat-through-2.9.0-integer-overflow-in-storeatts-via-attindex-and-nprefixes
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