Exploited

CVE-2025-20393

Cisco Secure Email Gateway · Email

Cisco Multiple Products Improper Input Validation Vulnerability

At a glance

Exploited. Added to CISA’s catalog of exploited vulnerabilities on December 17, 2025.

Affected product: Cisco Secure Email Gateway (category Email, indicative classification). Name in CISA’s catalog: Cisco Multiple Products.

What should I do?

Apply the patches or mitigations from Cisco; if none are available, stop using the product. For cloud services, follow the guidance from Cisco.

Deadline set by CISA for US federal agencies: 7 days (due December 24, 2025). It only binds those agencies, but it is a useful measure of urgency.

Cisco security advisories page (general page, not the advisory for this vulnerability)
The vendor’s specific advisory is listed in the NVD references: CVE-2025-20393 on the NVD website.

Original text of the required action (CISA)

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

Timeline

December 17, 2025 Vulnerability published Publication date (NVD)
December 17, 2025 Exploitation confirmed Added to CISA’s KEV catalog
December 24, 2025 CISA deadline Remediation deadline set for US federal agencies

The facts, with their sources

Exploitation confirmed: Yes, on December 17, 2025 Date added to the catalog of exploited vulnerabilities. Exploitation itself may have started earlier. Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
Ransomware: No known use to date That does not guarantee it is not being used: the information is not public. Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
Hunt for compromise: Not requested by CISA Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
CISA required action: Apply the patches or mitigations from Cisco; if none are available, stop using the product. For cloud services, follow the guidance from Cisco. Rewritten by this site from CISA’s original text. Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
CISA deadline: December 24, 2025, 7 days Set for US federal agencies: a measure of urgency, not an obligation elsewhere. Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
Vulnerability published: December 17, 2025 Source: National Vulnerability Database (NVD), collected September 29, 2026 at 15:00 UTC
Product according to CISA: Cisco Multiple Products Filed by this site under “Email” (indicative classification). Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H Technical detail of the score: attack vector, complexity, impact. Source: National Vulnerability Database (NVD), collected September 29, 2026 at 15:00 UTC

Severity and activity

10.0 / 10 CVSS severity: critical

Score from the vendor or CISA, relayed by the NVD. Collected Sep 29, 2026.

— Probability of exploitation in the next 30 days (EPSS)

FIRST’s EPSS model. Since exploitation is already confirmed, this figure is mostly useful to compare activity. Collected Sep 29, 2026.

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.

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.

Summary from CISA (KEV catalog).

CERT-FR advisories

No advisory among the latest CERT-FR publications this site follows. That does not mean there are none.

Information reused under the Open Licence 2.0 (Etalab); the date of last update is shown for each advisory. This site is neither affiliated with nor endorsed by ANSSI.

Sources for this page

CISA KEV catalog: exploitation, date added, required action, deadline, ransomware.
NVD (NIST): CVSS severity, publication date, description, vendor references.
EPSS (FIRST): probability of exploitation.
CERT-FR: advisories and alerts (in French).
Brand and category: indicative classification by this site (method).