CVE-2025-20393 is an improper input validation flaw (CWE-20) in Cisco Secure Email Gateway, Secure Email, AsyncOS software, and Web Manager appliances that lets attackers execute arbitrary commands with root privileges on the underlying operating system. The flaw is triggered when an affected appliance processes improperly validated input, though the CISA record does not specify the access vector or whether authentication is required. Successful exploitation yields full compromise of the appliance at the highest OS privilege level, which is significant because these devices sit in the email- and web-security path of enterprise networks. Organizations running these Cisco appliances are affected; CVSS has not yet been published and no public proof-of-concept is known. Exploitation is confirmed in the wild: CISA added the vulnerability to the KEV catalog on 2025-12-17, EPSS estimates a 29.9% chance of exploitation within 30 days (98th percentile), and ransomware use remains undetermined.
What to do: Apply the mitigations or updates Cisco specifies in its advisory for CVE-2025-20393 without waiting for a CVSS score; the CISA KEV entry directs users to vendor mitigations, applicable BOD 22-01 cloud-service guidance, or discontinuing use if mitigations are unavailable. Because this record contains no fixed-release details, check the Cisco PSIRT advisory for the exact patched AsyncOS and Web Manager versions before planning the upgrade. In the meantime, review appliance logs and configurations for signs of unexpected command execution or changes, since active exploitation is confirmed and ransomware use is still unknown.
Affected
Cisco Secure Email Gateway / Secure Email
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Cisco AsyncOS Software
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Cisco Web Manager appliance
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Estimated exposure
largeroughly tens of thousands of appliance deployments worldwide (exact installed base unpublished) — Cisco does not publish installed-base counts for this product line, so the estimate is inferred from its decades-long role as an enterprise email-security gateway typically deployed as one or a few appliances per organization, implying a…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
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.
CISA Known Exploited Vulnerability
Affected
Cisco Multiple Products
Required action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Actively exploited Cisco Secure Email Gateway zero-day CVE-2026-76461 lets crafted emails trigger SQL injection and root command execution; CISA added it to KEV.
Cisco released emergency patches for CVE-2026-76461, a critical SQL injection in Secure Email Gateway (physical and virtual) caused by insufficient validation in email parsing. Sending a crafted email with malicious SQL statements can yield arbitrary command execution with root privileges. Cisco was aware of active exploitation before the fixes, and CISA added the flaw to its KEV catalog; patched AsyncOS releases are 15.5.5-0141, 16.0.4-3021, and 16.5.0-780. Because successful exploits grant root, Cisco warns logs may be tampered with and advises checking external firewall/network logs and rebuilding virtual appliances with rotated credentials.
Attackers actively exploit critical Cisco Secure Email Gateway flaw CVE-2026-76461, turning a malicious email into unauthenticated root access.
Cisco Secure Email Gateway appliances are being actively exploited via CVE-2026-76461, a CVSS 9.8 AsyncOS flaw requiring no authentication—a crafted email can yield root command execution with no workarounds. Cisco's PSIRT became aware of active exploitation in September; some Secure Email Cloud customers showed indicators of compromise and all cloud devices were upgraded to AsyncOS 16.5.0-780. The bug is in CISA's KEV catalog with federal agencies ordered to remediate by September 17; Shadowserver counted 400+ exposed appliances. Fixes are available in AsyncOS 15.5.5-014, 16.0.4-302, and 16.5.0-780, and attackers with root may tamper with logs to hide activity.
Cisco patches actively exploited Secure Email Gateway zero-day CVE-2026-76461 enabling unauthenticated root command execution; CISA adds it to KEV.
Cisco disclosed that a critical zero-day (CVE-2026-76461) in the email parsing logic of AsyncOS for Secure Email Gateway is being actively exploited, allowing unauthenticated remote attackers to execute arbitrary SQL statements that lead to root-level command execution on virtual and physical appliances. CISA added the flaw to its KEV catalog and ordered federal agencies to patch within three days, by September 17. Cisco also patched four other critical SEG/SEWM vulnerabilities (CVE-2026-76440, CVE-2026-76441, CVE-2026-20353, CVE-2026-76443) with no evidence of exploitation, and shared IOCs including suspicious SQL statements in mail_logs.
Cisco warned customers on Monday that a zero-day vulnerability affecting Secure Email Gateway appliances has been exploited in the wild. The vulnerability is identified as CVE-2026-76461 and has a CVSS score of 9.8. Cisco describes it as an email parsing issue in AsyncOS software that can be exploited remotely and without authentication to execute arbitrary commands on the underlying operating…
Actively exploited zero-day SQL injection (CVE-2026-76461) in Cisco Secure Email Gateway allows unauthenticated root command execution; CISA ordered federal remediation by September 17.
Cisco confirmed attackers are exploiting zero-day CVE-2026-76461, an unauthenticated SQL injection in the email parsing logic of AsyncOS on Secure Email Gateway appliances (versions 16.5, 16.0, 15.5 and earlier) and Secure Email Cloud. Successful exploitation yields arbitrary SQL execution and root-level command execution on the underlying OS without user interaction. Cisco became aware of active exploitation in September 2025, has directly contacted affected cloud customers, and released fixed releases 15.5.5-014, 16.0.4-302, and 16.5.0-780. CISA added the flaw to its Known Exploited Vulnerabilities catalog and required federal civilian agencies to patch by September 17 and hunt for compromise.