CVE-2015-6309 in Email Security Appliance
Summary
by MITRE
Cisco Email Security Appliance (ESA) 8.5.6-106 and 9.6.0-042 allows remote authenticated users to cause a denial of service (file-descriptor consumption and device reload) via crafted HTTP requests, aka Bug ID CSCuw32211.
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Analysis
by VulDB Data Team • 06/20/2022
The Cisco Email Security Appliance ESA represents a critical component in enterprise email security infrastructure, serving as a gateway for filtering and protecting organizations against malicious email traffic. This vulnerability specifically affects versions 8.5.6-106 and 9.6.0-042 of the ESA software, making it a significant concern for organizations relying on these systems for email protection. The flaw manifests as a denial of service condition that can be triggered by remote authenticated users, highlighting the potential for both internal and external attackers to disrupt email services. The vulnerability operates through crafted HTTP requests that exploit a fundamental flaw in the appliance's resource management mechanisms, ultimately leading to complete device reloads that can severely impact business operations.
The technical implementation of this vulnerability involves an insufficient resource management flaw that results in file descriptor consumption. When authenticated users send specifically crafted HTTP requests to the ESA, the system fails to properly manage its file descriptors, leading to progressive consumption of available file descriptor resources. This type of vulnerability maps directly to CWE-404, which describes improper resource management where a system fails to properly handle or release resources, and can be categorized under the broader ATT&CK technique T1499.3 for network denial of service. The crafted HTTP requests exploit a weakness in the ESA's input validation and resource allocation processes, where the appliance does not adequately sanitize or limit the number of file descriptors that can be consumed during HTTP request processing.
The operational impact of this vulnerability extends beyond simple service disruption, as it can cause complete device reloads that require manual intervention and can result in extended downtime for email services. Organizations may experience significant business disruption when email communication becomes unavailable, potentially affecting customer service, internal communications, and critical business processes that depend on email infrastructure. The remote authentication requirement means that attackers do not need physical access to the device, and can potentially exploit this vulnerability from anywhere on the network, making it particularly dangerous in environments where the ESA is accessible from untrusted networks. The device reload process can take considerable time, during which email services are completely unavailable, potentially causing cascading effects throughout the organization's communication systems.
Mitigation strategies for this vulnerability should focus on immediate patching of affected systems, implementing network segmentation to limit access to the ESA, and monitoring for suspicious HTTP traffic patterns. Organizations should prioritize applying the official Cisco security patches released for this vulnerability, as they address the root cause of the file descriptor consumption issue. Network administrators should also consider implementing access controls that limit which users can authenticate to the ESA and restrict HTTP access to only necessary administrative functions. The implementation of intrusion detection systems can help identify and alert on the specific patterns of crafted HTTP requests that trigger this vulnerability, providing early warning of potential exploitation attempts. Additionally, regular security assessments and vulnerability scanning should be conducted to identify any other potential weaknesses in the email security infrastructure that could be exploited in similar fashion, ensuring comprehensive protection against this and related threats.