CVE-2017-3800 in Email Security Appliance
Summary
by MITRE
A vulnerability in the content scanning engine of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) could allow an unauthenticated, remote attacker to bypass configured message or content filters on the device. Affected Products: This vulnerability affects all releases prior to the first fixed release of Cisco AsyncOS Software for Cisco Email Security Appliances, both virtual and hardware appliances, if the software is configured to apply a message filter or content filter to incoming email attachments. The vulnerability is not limited to any specific rules or actions for a message filter or content filter. More Information: CSCuz16076. Known Affected Releases: 9.7.1-066 9.7.1-HP2-207 9.8.5-085. Known Fixed Releases: 10.0.1-083 10.0.1-087.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability described in CVE-2017-3800 represents a critical security flaw within the content scanning engine of Cisco AsyncOS Software deployed on Email Security Appliances. This weakness allows unauthenticated remote attackers to bypass configured message and content filters, effectively undermining the core security posture of email protection systems. The vulnerability specifically targets the filtering mechanisms that are designed to prevent malicious content from entering corporate networks through email attachments, creating a significant attack surface that could be exploited by threat actors without requiring any credentials or privileged access.
The technical nature of this flaw stems from improper validation within the content scanning engine's processing logic. When email attachments are received by the ESA, the system should apply configured filters to identify and block potentially harmful content according to organizational security policies. However, the vulnerability allows attackers to craft specific email messages that can circumvent these protective measures through a flaw in the engine's content evaluation process. This bypass capability is not restricted to particular filter rules or content types, meaning that attackers can exploit the vulnerability across all configured message and content filtering policies, rendering the entire filtering system ineffective.
The operational impact of this vulnerability extends beyond simple bypass of email security controls. Organizations relying on Cisco ESA appliances for email protection face a heightened risk of malware delivery, data exfiltration attempts, and other malicious activities that could compromise network security. The vulnerability affects both virtual and hardware implementations of the software, indicating that the flaw exists at the software level rather than being hardware-specific. Given that the affected releases include versions 9.7.1-066, 9.7.1-HP2-207, and 9.8.5-085, organizations using these specific versions are particularly at risk, as the vulnerability has been confirmed to exist in these software releases prior to the fixed versions 10.0.1-083 and 10.0.1-087.
This vulnerability aligns with CWE-284, which addresses improper access control mechanisms, and demonstrates how content filtering systems can be compromised through insufficient validation of incoming message content. From an ATT&CK framework perspective, this vulnerability maps to techniques involving bypassing security controls and privilege escalation, as attackers can effectively circumvent the email security controls that should protect against malicious attachments. The implications of this flaw extend to broader security operations, as it represents a fundamental failure in the email security appliance's ability to enforce configured security policies, potentially allowing threat actors to deliver phishing emails, malware payloads, or other malicious content directly to end users without detection.
Organizations affected by this vulnerability should prioritize immediate remediation through the application of the fixed software releases mentioned in the advisory. The mitigation strategy should include comprehensive testing of the updated software to ensure that the fix properly addresses the bypass capability while maintaining all existing email security functionality. Additionally, security teams should conduct thorough assessments of their email security configurations to identify any potential exploitation attempts that may have occurred during the vulnerability's active period. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date security software and the potential consequences of failing to apply security patches in a timely manner, particularly for core security infrastructure components like email security appliances that form the first line of defense against email-based attacks.