CVE-2015-4236 in Email Security Appliance
Summary
by MITRE
Cisco AsyncOS on Email Security Appliance (ESA) devices with software 8.5.6-073, 8.5.6-074, and 9.0.0-461, when clustering is enabled, allows remote attackers to cause a denial of service (clustering and SSH outage) via a packet flood, aka Bug IDs CSCur13704 and CSCuq05636.
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Analysis
by VulDB Data Team • 05/31/2022
The vulnerability identified as CVE-2015-4236 affects Cisco AsyncOS email security appliances with specific software versions when clustering functionality is enabled. This represents a critical denial of service weakness that can be exploited remotely through packet flooding attacks, potentially disrupting both clustering operations and secure shell access to affected systems. The vulnerability specifically impacts devices running software versions 8.5.6-073, 8.5.6-074, and 9.0.0-461, making it particularly concerning for organizations relying on Cisco email security infrastructure for their messaging security needs.
The technical flaw manifests in how the affected Cisco ESA devices handle packet flood attacks when clustering is active. When subjected to excessive packet traffic, the system experiences a cascade failure that affects both the clustering mechanism and SSH connectivity, effectively rendering the appliance unable to properly function within its intended security role. This vulnerability operates at the network protocol level, exploiting weaknesses in packet processing and resource management within the AsyncOS operating system that powers the email security appliances. The attack vector requires only network access to the device, making it particularly dangerous as it can be executed from external networks without requiring authentication credentials.
The operational impact of this vulnerability extends beyond simple service interruption, as it compromises the fundamental security infrastructure that organizations depend upon for email protection. When clustering is disrupted, the appliance loses its ability to maintain synchronized operations with other devices in the cluster, potentially leading to inconsistent security policies and gaps in email protection. The SSH outage further compounds the issue by preventing administrators from remotely accessing and managing the affected systems, creating a situation where security teams cannot respond to the incident or implement corrective measures. This vulnerability directly affects the availability and integrity of email security services, potentially exposing organizations to increased risk of email-borne threats during the period of disruption.
Organizations affected by this vulnerability should implement immediate mitigations including applying the relevant Cisco security patches and updates, disabling clustering functionality if it is not essential for their operations, and implementing network-level controls to filter and limit packet flood attacks. Network administrators should also consider implementing intrusion detection systems to monitor for unusual traffic patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-400, which addresses unchecked resource consumption, and maps to ATT&CK technique T1498, which covers network denial of service attacks. Additionally, this vulnerability demonstrates the importance of proper input validation and resource management in network security appliances, as outlined in various cybersecurity frameworks and standards including NIST SP 800-34 and ISO/IEC 27001. Organizations should also conduct comprehensive security assessments to identify any other potentially vulnerable systems within their email security infrastructure and ensure that their incident response procedures include specific protocols for handling clustering-related denial of service conditions.