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CISA KEV · ACTIVELY EXPLOITED
CRITICAL severity

CVE-2025-20393 — Asyncos

CRITICAL

CVE-2025-20393 is a critical-severity (CVSS 10) Improper Input Validation vulnerability in cisco asyncos. It is in CISA's Known Exploited Vulnerabilities catalog (added 2025-12-17) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.

A vulnerability in the Spam Quarantine feature of Cisco AsyncOS Software for Cisco Secure Email Gateway and Cisco Secure Email and Web Manager could allow an unauthenticated, remote…

Published
Updated
Affected
1 product
Patched
See advisory
Exploits
None indexed
Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

  • Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2025-12-17. Federal agencies were required to remediate by 2025-12-24.
  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2025-20393.

EPSS Exploitation Probability

via FIRST.org ↗
32.4%probability of exploitation in next 30 days
Moderate Risk0.00%
Lower risk than most CVEs98th percentile — riskier than 98% of all scored CVEsHighest risk
0.00%13.4%26.8%40.2%6.3%32.4%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2025-20393 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.

Description

A vulnerability in the Spam Quarantine feature of Cisco AsyncOS Software for Cisco Secure Email Gateway and Cisco Secure Email and Web Manager could allow an unauthenticated, remote attacker to execute arbitrary system commands on an affected device with root privileges.

This vulnerability is due to insufficient validation of HTTP requests by the Spam Quarantine feature. An attacker could exploit this vulnerability by sending a crafted HTTP request to the affected device. A successful exploit could allow the attacker to execute arbitrary commands on the underlying operating system with root privileges.

Affected Products

1 product · 6 configurations
OS
asyncoscisco
≥ 16.0 && < 16.0.4-010
range

Detection & mitigation playbook

Vendor / appliance

  1. Detect

    Inventory every cisco asyncos deployment and check each version against the affected-products list above.

  2. Fix

    Apply the cisco asyncos security patch or hotfix for CVE-2025-20393 on the affected version, following the vendor advisory for your exact build.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Frequently Asked Questions

A vulnerability in the Spam Quarantine feature of Cisco AsyncOS Software for Cisco Secure Email Gateway and Cisco Secure Email and Web Manager could allow an unauthenticated, remote attacker to execute arbitrary system commands on an affected device with root privileges. This vulnerability is due to insufficient validation of HTTP requests by the Spam Quarantine feature. An attacker could exploit this vulnerability by sending a crafted HTTP request to the affected device. A successful exploit could allow the attacker to execute arbitrary commands on the underlying operating system with&nbsp
O3 Security · Runtime Protection

Is CVE-2025-20393 being exploited in your environment?

Detect and block the exploit chain at execution, on systems you cannot patch yet.

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Actively Exploited: CVE-2025-20393: Asyncos (Critical 10)