Known exploited vulnerability · CISA KEV

CVE-2025-20393: Cisco Multiple Products Improper Input Validation Vulnerability

Cisco Secure Email Gateway, Secure Email, AsyncOS Software, and Web Manager appliances contains an improper input validation vulnerability that allows threat actors to execute arbitrary commands with root privileges on the underlying operating system of an affected appliance.

CVE-2025-20393

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2025-12-17: attackers are using it right now.

CISA KEV: Listed; Added 2025-12-17 · federal fix-by 2025-12-24
EPSS (30 days): 32%; Higher than 98% of CVEs · 2026-11-01
CVSS v3.1: 10.0 Critical; CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

What CISA says

Cisco Multiple Products Improper Input Validation Vulnerability

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

NVD description · published 2025-12-17

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.

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How to check if you are exposed to CVE-2025-20393

Find every Cisco Multiple Products system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2025-20393.

US federal agencies had to fix this by 2025-12-24. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Affected versions

Versions the National Vulnerability Database lists as vulnerable to CVE-2025-20393. Check the vendor advisory for the exact fixed builds before you sign anything off.

Product	Vulnerable versions
Cisco Asyncos	before 15.0.5-016; from 15.5 before 15.5.4-012; from 16.0 before 16.0.4-016; before 15.0.2-007; from 15.5 before 15.5.4-007; from 16.0 before 16.0.4-010

Timeline

2025-12-17 · Published in the National Vulnerability Database
2025-12-17 · Added to CISA's Known Exploited Vulnerabilities catalog, the same day it was published
2025-12-24 · Fix-by date for US federal agencies, passed 312 days ago

Vendor advisories and fixes

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sma-attack-N9bf4

Weakness type

CWE-20

More exploited Cisco vulnerabilities

CISA lists 102 exploited Cisco vulnerabilities. The closest matches:

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Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.