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Cisco Warns of Seven ClamAV Flaws, Two With Public PoCs

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CVE-2026-20337 CVE-2026-20338 ClamAV Parser Flaws DoS Risk Cisco Secure Endpoint

Overview

Cisco disclosed seven ClamAV vulnerabilities affecting the Secure Endpoint Connector. The flaws exist in ClamAV parsers responsible for processing ZIP, GPT, PESpin, PDF, Mach-O, and XAR formats.

An unauthenticated remote attacker could submit a specially crafted file for scanning and potentially terminate the ClamAV scanning process, causing a denial-of-service (DoS) condition.

Technical Details

CVE-2026-20337 involves improper boundary checking in the ZIP parser and can result in an out-of-bounds write. CVE-2026-20338 involves improper memory handling in ZIP processing.

Additional vulnerabilities impact GPT, PDF, Mach-O, and XAR parsing and involve memory corruption or improper boundary handling. Cisco assigns CVSS vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, indicating remote exploitation without authentication or user interaction, with high availability impact.

Technical Specifications

Attribute Details
Advisory Scope Seven ClamAV vulnerabilities in Cisco Secure Endpoint Connector context
Key CVEs Highlighted CVE-2026-20337, CVE-2026-20338
Vulnerability Class Boundary-checking and memory-handling flaws in file parsers
Affected Parser Formats ZIP, GPT, PESpin, PDF, Mach-O, XAR
Attack Vector Network-submitted file to scanning workflow
Authentication Requirement None
User Interaction Requirement None
Primary Impact ClamAV process termination (DoS)
CVSS Vector (Cisco) AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Known Public Exploit Status Public PoCs reported for two ZIP-related vulnerabilities

Affected Products

  • Cisco Secure Endpoint Connector components using vulnerable ClamAV parsing paths
  • ClamAV deployments prior to fixed release 1.5.4 in applicable environments
  • Windows connector environments where scanner process privilege context can increase operational risk
  • File-scanning workflows that ingest untrusted archives and document formats

Attack Scenario

  1. Attacker crafts a malicious archive or file targeting a vulnerable parser.
  2. The file is sent or uploaded through a channel that triggers Cisco Secure Endpoint or ClamAV scanning.
  3. Vulnerable parser code processes malformed content.
  4. Memory corruption or boundary-handling failure occurs.
  5. ClamAV scanning process terminates unexpectedly.
  6. Malware-scanning and endpoint-protection visibility is disrupted.
  7. Attacker benefits from degraded detection coverage while malicious activity proceeds.

Impact Assessment

  • No primary evidence of direct integrity manipulation was disclosed for these bugs
  • Defensive integrity degrades indirectly when scanning services crash and controls are bypassed
  • Security operations decisions may be impacted by reduced trust in scan coverage during outages
  • No direct confidentiality loss is the main demonstrated effect in current reporting
  • Reduced malware detection can indirectly expose sensitive systems to follow-on compromise
  • Interrupted scanning may delay detection of payloads intended for data theft stages
  • Primary demonstrated impact is denial of service via ClamAV process termination
  • Malware scanning operations can be interrupted, reducing endpoint protection continuity
  • Risk is more significant on Windows where the scanner process may run with elevated privileges

Mitigation Strategies

Immediate Remediation

  • Apply Cisco security updates for affected Secure Endpoint Connector versions as soon as available.
  • Upgrade ClamAV components to version 1.5.4 where applicable.
  • Prioritize patch rollout for Windows endpoints due to higher process-privilege risk.

Exposure Reduction

  • Identify all connectors and scanning paths that process untrusted archives and documents.
  • Validate that update channels are functioning for endpoint connectors and signature engines.
  • Ensure unsupported or delayed-update endpoints are isolated from high-risk ingestion flows.

Monitoring and Detection

  • Monitor for abnormal ClamAV process crashes, restarts, or scan-service instability.
  • Investigate suspicious archive or file submissions that correlate with scanner termination events.
  • Track endpoint telemetry for detection gaps following scan-engine failures.

Response Actions

  • Treat repeated scan-process crashes as potential exploitation attempts and trigger incident triage.
  • Increase compensating controls temporarily if patching is delayed.
  • Confirm remediation by validating connector and ClamAV versions after deployment.

Resources and References

Public Reporting

Last Updated: August 12, 2026