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CVE-2026-66046— Expat Denial of Service via storeAtts() Quadratic Complexity

Quick assessment

Affected
libexpat project 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 漏洞至 2.8.3 版本存在一个拒绝服务漏洞，该漏洞源于 xmlparse.c 中的 storeAtts() 函数中具有二次算法复杂度。当处理 N 个指定属性且其值未标准化时，会触发对 elementType->defaultAtts 的 O(N^2) 线性扫描，以判断 CDATA 状态。远程未认证的攻击者可以向解析不受信任 XML 的应用程序提供一个结构良好但大小为几兆字节的单一 XML 文档，从而导致过度的 CPU 消耗，引发拒绝服务攻击。此攻击无需认证、外部实体解析或非默认解析器选项即可实现。

CVSS 7.5 · High EPSS 0.68% · P49

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
libexpat project libexpat ≤ 2.8.3 affected
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I. Basic Information for CVE-2026-66046

Vulnerability Information
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Vulnerability Title
Expat Denial of Service via storeAtts() Quadratic Complexity
Source: CVE Program / CVE List V5
Vulnerability Description
Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType->defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.
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
算法复杂性
Source: CVE Program / CVE List V5

Affected Products

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

II. Public POCs for CVE-2026-66046

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8164 chars
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III. Intelligence Information for CVE-2026-66046

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Patches & Fixes for CVE-2026-66046 (1)

Vendor Advisories for CVE-2026-66046 (1)

IV. Related Vulnerabilities

Same product: libexpat
Same vendor: libexpat project
Same weakness: CWE-407

V. Comments for CVE-2026-66046

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