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A critical zero-day flaw in Cisco Secure Email Gateway and Cisco Secure Email and Web Manager devices is causing concern among security researchers. With over 120 vulnerable devices already identified and actively exploited by attackers, the situation is alarming to say the least.
The vulnerability, identified as CVE-2025-20393, has not yet been patched. This means that organizations that rely on these systems to protect their networks from phishing and malware attacks are at risk of compromise.
According to threat intelligence provided by the Shadowserver Foundation , the vulnerable devices represent a subset of more than 650 Cisco email security devices exposed and accessible over the Internet.
CVE-2025-20393 targets Cisco’s email security infrastructure, which enterprises use to inspect inbound and outbound email traffic for threats.
While specific technical details on the exploitation method remain limited to prevent widespread abuse, confirmation of active exploitation indicates that threat actors are already exploiting this weakness to compromise vulnerable systems.
Cisco has acknowledged the vulnerability and published a security advisory urging organizations to implement immediate defensive measures . The networking giant advises affected customers to review their security configurations and apply temporary mitigations until a permanent fix is available. Businesses can access detailed guidance through Cisco’s Security Advisory portal .
The situation highlights the ongoing challenges organizations face due to zero-day vulnerabilities, particularly in critical infrastructure components such as email gateways. These devices are at a crucial point in corporate networks, handling sensitive communications and serving as the primary defense against email-borne threats. A successful compromise could allow attackers to intercept confidential communications, distribute ransomware, or establish persistent access to the network.
Cisco is actively working to fix the flaw, which, as reported in their bulletin, appears to have a base score of 10.
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