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CVE-2026-76641— Expat Out-of-Bounds Read via dtdCopy

Quick assessment

Affected
libexpat libexpat
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Expat 2.8.3 及之前版本存在一个越界读取漏洞，攻击者可通过处理由 XML_ExternalEntityParserCreate 创建的外部实体解析器中的 XML 文件，触发内存破坏。ELEMENT_TYPE 成员之间的结构体大小不匹配导致 storeAtts 函数在分配内存边界之外读取 attIndex 成员，进而引发非 CDATA 属性中空白字符无法正确归一化，或野指针解引用导致段错误（segfault）。该漏洞由 CVE-2026-66046 的修复引入。

CVSS 7.5 · High EPSS 0.34% · P27

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
libexpat libexpat ≤ 2.8.3 affected
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I. Basic Information for CVE-2026-76641

Vulnerability Information
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Vulnerability Title
Expat Out-of-Bounds Read via dtdCopy
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
libexpat libexpat 0 ~ 2.8.3 -

II. Public POCs for CVE-2026-76641

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8775 chars
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III. Intelligence Information for CVE-2026-76641

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Patches & Fixes for CVE-2026-76641 (2)

Vendor Advisories for CVE-2026-76641 (1)

IV. Related Vulnerabilities

Same product: libexpat
Same weakness: CWE-125

V. Comments for CVE-2026-76641

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