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libexpat EUVDEUVD-2026-60821

| CVE-2026-66046 HIGH
Inefficient Algorithmic Complexity (CWE-407)
2026-08-18 VulnCheck GHSA-m3rp-25vq-jfcv
Denial Of Service Libexpat Suse
8.7
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
8.7 HIGH
CVSS: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
vuln.today AI
7.5 HIGH

Network-reachable with no auth, no user interaction, and no complexity; impact is pure availability via CPU exhaustion with no confidentiality or integrity effects.

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

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

CVSS: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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 18, 2026 - 15:20 vuln.today
Analysis Generated
Aug 18, 2026 - 15:20 vuln.today
CVE Published
Aug 18, 2026 - 14:10 cve.org
HIGH 8.7

DescriptionCVE.org

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.

AnalysisAI

Denial of service in libexpat through 2.8.3 stems from quadratic CPU complexity in the storeAtts() XML attribute processing function, enabling remote unauthenticated attackers to exhaust server CPU with a compact, well-formed XML document. The flaw-closely related to CVE-2026-45186 fixed in Expat 2.8.1-requires no authentication, no external entity resolution, and no non-default parser options to trigger, and is significantly amplified when XML payloads are compression-wrapped. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Send crafted HTTP request with large XML body
Delivery
Deliver element with N attributes with non-normalized values
Exploit
Trigger O(N^2) linear scan in storeAtts() per attribute
Execution
Exhaust CPU cycles on parsing thread
Impact
Deny service to legitimate users
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Vulnerability AssessmentAI

Exploitation Exploitation requires the target application to accept untrusted XML and pass it synchronously to libexpat for parsing via a network-accessible interface. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N) accurately reflects the low exploitation bar: no authentication, no complexity, no special trigger beyond a well-formed XML document with many non-normalized attributes. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker crafts a well-formed XML document of several megabytes containing a large element with many attributes carrying non-normalized values and submits it to any HTTP endpoint-such as an XML-based API or SOAP service-that passes untrusted input directly to libexpat for synchronous parsing. The parser's O(N^2) scan of default attribute metadata pins one or more CPU cores for the duration of the parse, degrading or denying service to concurrent legitimate users without triggering any authentication check or error condition. …
Remediation The upstream fix is available as GitHub PR #1321 (https://github.com/libexpat/libexpat/pull/1321) targeting libexpat 2.8.4; however, the changelog entry carries placeholder dates ('XXX XXXXXX XX XXXX'), meaning a packaged 2.8.4 release has not been confirmed at time of analysis-patch status is 'upstream fix available (PR/commit); released patched version not independently confirmed.' Organizations should monitor the libexpat GitHub releases page and their OS distribution channels (Debian, Red Hat, Ubuntu, Alpine, Homebrew) for backported security updates. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: identify and document all systems and applications using libexpat (check OS package inventories, application dependencies, and embedded libraries), determine which processes handle untrusted or external XML, and enable CPU/resource monitoring for anomalies in XML processing workflows. …

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SLES15-SP5-CHOST-BYOS-SAP-CCloud Not-Affected
SLES15-SP5-CHOST-BYOS-SAP-CCloud Not-Affected
SLES15-SP6-CHOST-BYOS Not-Affected
SLES15-SP6-CHOST-BYOS-Aliyun Not-Affected
SLES15-SP6-CHOST-BYOS-Azure Not-Affected

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EUVD-2026-60821 vulnerability details – vuln.today
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