CVE-2016-1438 in AsyncOS
Summary
by MITRE
Cisco AsyncOS 9.7.0-125 on Email Security Appliance (ESA) devices allows remote attackers to bypass intended spam filtering via crafted executable content in a ZIP archive, aka Bug ID CSCuy39210.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 08/24/2022
The vulnerability identified as CVE-2016-1438 affects Cisco AsyncOS version 9.7.0-125 running on Email Security Appliance devices, representing a critical security flaw in email content filtering mechanisms. This vulnerability enables remote attackers to circumvent the intended spam filtering protections by exploiting a weakness in how the system processes executable content within ZIP archive files. The issue stems from insufficient validation of file types and content within compressed archives, allowing malicious payloads to bypass security controls that should prevent the delivery of potentially harmful executable files through email channels.
The technical flaw manifests in the ESA's handling of ZIP archive contents where the system fails to properly validate or sanitize executable files embedded within compressed archives. When a ZIP file containing malicious executables is processed by the email security appliance, the system does not adequately inspect the archive contents to identify and block potentially harmful file types. This weakness specifically affects the spam filtering logic that should prevent the delivery of executable content through email, creating a pathway for attackers to deliver malware or other malicious payloads disguised as legitimate email attachments. The vulnerability operates at the application layer and can be exploited remotely without requiring authentication or privileged access to the system.
The operational impact of this vulnerability extends beyond simple spam bypass, as it represents a significant weakening of email security controls that organizations rely upon to protect against malware distribution and phishing attacks. Organizations using affected ESA devices face increased risk of email-borne malware infections, as attackers can now deliver executable content through ZIP archives that would normally be blocked by the spam filtering system. This creates a persistent threat vector where malicious actors can craft email messages containing ZIP archives with embedded executables, potentially leading to successful compromise of endpoints, data exfiltration, or lateral movement within networks. The vulnerability affects the core security functionality of the email appliance, undermining the trust model that organizations place in their email security infrastructure.
Mitigation strategies for CVE-2016-1438 should focus on immediate patching of affected devices to the latest Cisco AsyncOS releases that address the validation flaw in ZIP archive processing. Organizations should implement additional network-level controls such as blocking or quarantining ZIP files at network boundaries, and enhancing email security policies to restrict executable content delivery regardless of archive status. Network administrators should also consider implementing more robust content inspection mechanisms and monitoring for unusual patterns of ZIP file processing within email traffic. The vulnerability aligns with CWE-20 Improper Input Validation and relates to ATT&CK technique T1193 Spearphishing Attachment, where attackers use email attachments as initial access vectors. Security teams should also conduct thorough vulnerability assessments of their email security infrastructure to identify potential similar weaknesses in other components of their email filtering stack, as this flaw demonstrates a critical gap in archive content validation that could affect other security controls.