CVE-2026-66046Public exploitNetwork attack vector

CPU exhaustion via storeAtts CDATA lookup

Published Aug 18, 2026 · Updated Aug 20, 2026

Denial of service in Expat through 2.8.3 allows remote attackers to exhaust CPU via a crafted XML document with many normalized attributes. In xmlparse.c, storeAtts() linearly scans elementType->defaultAtts to determine whether each maybeTokenized attribute is CDATA, so processing many specified attributes turns one parse into quadratic work. Exposure requires an application that parses untrusted XML with Expat; no authentication, external entity resolution, or non-default parser options are required, and the result is service interruption from excessive CPU use rather than memory corruption or code execution.

CVSS severity7.5
High
EPSS probability0.59%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in Expat through 2.8.3 allows remote attackers to exhaust CPU via a crafted XML document with many normalized attributes. In xmlparse.c, storeAtts() linearly scans elementType->defaultAtts to determine whether each maybeTokenized attribute is CDATA, so processing many specified attributes turns one parse into quadratic work. Exposure requires an application that parses untrusted XML with Expat; no authentication, external entity resolution, or non-default parser options are required, and the result is service interruption from excessive CPU use rather than memory corruption or code execution.

The record

CVE
CVE-2026-66046
Published
Aug 18, 2026
Updated
Aug 20, 2026
Vendor
Expat Project
Product
libexpat
Classifications
CWE-407, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=2.8.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Expat Project · libexpatversion=0 <=2.8.3

Published CVSS scores

8.7VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-407Inefficient Algorithmic Complexity
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo