CVE-2026-76641: libexpat Out-of-bounds Read
Vulnerability summary
CVE-2026-76641 is a high (CVSS 8.7) Out-of-bounds Read vulnerability in libexpat. EPSS estimates a 0.35% chance of exploitation in the next 30 days, higher than 27.5% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 10 · Related 8Timeline
- 20-08-2026PublishedVulnerability first disclosed.
- 01-10-2026Last modifiedVulnerability information updated.
Description
Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for CVE-2026-66046.
CVSS metrics
7 scores · 4 sources · 2 versions- OSV · AlpineEcosystem advisory · calculated8.7HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · UbuntuEcosystem advisory · calculated8.7HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- NVDNIST8.7HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.35%
Chance of exploitation in the next 30 days
Percentile
28%
Versus all other CVEs
30-day change
0.00 pp
From 0.35% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Ubuntu16 products
- ayttmAll versions (No fix recorded)
- cableswigAll versions (No fix recorded)
- cadaverAll versions (No fix recorded)
- coin3All versions (No fix recorded)
- expat< 2.1.0-4ubuntu1.4+esm13 | < 2.1.0-7ubuntu0.16.04.5+esm14 | < 2.2.5-3ubuntu0.9+esm5 | < 2.2.9-1ubuntu0.8+esm3 | < 2.4.7-1ubuntu0.9 | < 2.6.1-2ubuntu0.6 | < 2.7.4-1ubuntu0.2
Alpine1 product
- expat< 2.8.4-r0
Libexpat1 product
- libexpat≤ 2.8.3
3 vendors · 18 products
References
8 links- www.vulncheck.com/advisories/expat-out-of-bounds-read-via-dtdcopyThird Party Advisory
