CVE-2016-1480 in Email Security Appliance
Summary
by MITRE
A vulnerability in the Multipurpose Internet Mail Extensions (MIME) scanner of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) and Web Security Appliances (WSA) could allow an unauthenticated, remote attacker to bypass configured user filters on the device. Affected Products: all releases prior to the first fixed release of Cisco AsyncOS Software for Cisco ESA and Cisco WSA, both virtual and hardware appliances, if the software is configured with message or content filters to scan incoming email attachments. More Information: CSCuw03606, CSCux59734. Known Affected Releases: 8.0.0-000 8.5.6-106 9.0.0-000 9.1.0-032 9.6.0-042 9.5.0-444 WSA10.0.0-000. Known Fixed Releases: 9.1.1-038 9.7.1-066.
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Analysis
by VulDB Data Team • 10/14/2024
The vulnerability described in CVE-2016-1480 represents a critical security flaw within the MIME scanning functionality of Cisco AsyncOS software that operates on both Email Security Appliances and Web Security Appliances. This issue stems from improper validation of email attachment content during the scanning process, creating a pathway for malicious actors to circumvent configured security policies without requiring authentication or prior access to the system. The flaw specifically impacts organizations that rely on these appliances for content filtering and email security, potentially allowing unauthorized bypass of attachment scanning rules that should prevent malicious files from entering the network.
The technical implementation of this vulnerability resides in the MIME parser's handling of malformed or specially crafted email attachments that contain multiple content types or nested structures. When the system processes these complex attachments, the scanner fails to properly validate the content boundaries and MIME type declarations, enabling attackers to craft emails that appear to comply with security policies while actually containing hidden malicious content. This behavior aligns with CWE-129, which addresses improper validation of input boundaries, and represents a classic case of insufficient input sanitization that allows crafted data to bypass security controls. The vulnerability operates at the content inspection layer where the system should be enforcing strict filtering rules but instead permits certain attachment types to slip through undetected.
The operational impact of this vulnerability extends beyond simple bypass of security policies, creating significant risk for organizations that depend on these appliances for email and web content filtering. An unauthenticated remote attacker can exploit this weakness to deliver malicious payloads that would normally be blocked by the appliance's configured filters, potentially leading to data breaches, malware infections, and network compromise. The vulnerability affects all versions prior to the specified fixed releases, indicating that organizations running these appliances in production environments may be exposed to risk if they have not applied the necessary security patches. This represents a critical failure in the principle of least privilege and defense in depth, as the system fails to maintain its role as a security barrier between external threats and internal network resources.
Organizations affected by this vulnerability should immediately implement the recommended remediation measures, including upgrading to the fixed releases specified in the advisory. The mitigation strategy should also include comprehensive network monitoring to detect potential exploitation attempts and review of existing security policies to ensure that multiple layers of protection are maintained. Additional defensive measures may include implementing additional email security controls, such as sandboxing suspicious attachments, deploying network segmentation to limit lateral movement, and establishing incident response procedures for potential exploitation. The vulnerability demonstrates the importance of regular security updates and the necessity of maintaining current threat intelligence to address emerging risks in network security infrastructure. This issue highlights the critical need for robust input validation and boundary checking in security appliances, as outlined in the ATT&CK framework's techniques for bypassing security controls and privilege escalation through software vulnerabilities.