CVE-2016-1481 in Email Security Appliance
Summary
by MITRE
A vulnerability in the email message filtering feature of Cisco AsyncOS Software for Cisco Email Security Appliances could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected 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 that contains certain rules. More Information: CSCux59873. Known Affected Releases: 8.5.6-106 9.1.0-032 9.7.0-125. 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-2016-1481 represents a critical denial of service weakness within Cisco AsyncOS Software that specifically targets the email message filtering functionality of Cisco Email Security Appliances. This flaw affects both virtual and hardware implementations of the email security infrastructure, creating a significant operational risk for organizations relying on these systems for email protection. The vulnerability manifests when the software processes certain message filter rules, potentially allowing an unauthenticated remote attacker to disrupt normal email operations without requiring any privileged access or credentials. The impact extends across multiple software versions, with affected releases including 8.5.6-106, 9.1.0-032, and 9.7.0-125, while fixed releases are identified as 9.1.1-038 and 9.7.1-066, indicating a pattern of remediation across different software branches.
The technical mechanism behind this vulnerability involves the improper handling of specific message filter rules within the email security appliance's processing pipeline. When these particular rules are applied to email filtering configurations, the system fails to properly validate or process incoming email messages, leading to a condition where the appliance becomes unresponsive or crashes. This behavior aligns with common denial of service attack patterns where malformed inputs or specific processing conditions cause system resources to become exhausted or processing threads to fail. The vulnerability's classification as a remote attack vector means that malicious actors can exploit this weakness from outside the network perimeter, potentially causing widespread disruption to email services across organizations that depend on Cisco Email Security Appliances for their email infrastructure.
From an operational impact perspective, this vulnerability creates significant business continuity concerns for organizations using Cisco email security appliances, as the DoS condition can result in complete email service disruption. The attack does not require authentication, making it particularly dangerous as it can be exploited by anyone with network access to the affected appliance. Organizations may experience extended downtime while restoring email services, potentially affecting communication workflows and productivity across their enterprise. The vulnerability's presence in multiple software releases indicates that it was a persistent issue that required coordinated remediation efforts across different product lines. Network administrators may face challenges in identifying which specific filter rules trigger the vulnerability, requiring careful analysis and testing of existing email filtering configurations.
Security mitigations for CVE-2016-1481 primarily involve applying the vendor-provided software updates to the affected Cisco Email Security Appliances. Organizations should prioritize upgrading to the fixed releases 9.1.1-038 or 9.7.1-066, which contain patches addressing the message filtering processing flaw. Additionally, network administrators should review existing email filtering rules to identify and temporarily disable any rules that match the vulnerable patterns described in the Cisco security advisory. This approach reduces the attack surface while implementing the permanent fix. The vulnerability's characteristics align with ATT&CK technique T1499.004 for network denial of service, which involves causing a network service to become unavailable through various technical means. Organizations should also consider implementing network segmentation to limit access to email security appliances and monitor for unusual traffic patterns that might indicate exploitation attempts. The weakness demonstrates a clear relationship to CWE-400, which covers unspecified errors in input handling that can lead to resource exhaustion and system instability, reinforcing the importance of proper input validation and error handling within security appliance software.