CVE-2015-0605 in AsyncOS
Summary
by MITRE
The uuencode inspection engine in Cisco AsyncOS on Cisco Email Security Appliance (ESA) devices 8.5 and earlier allows remote attackers to bypass intended content restrictions via a crafted e-mail attachment with uuencode encoding, aka Bug ID CSCzv54343.
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Analysis
by VulDB Data Team • 06/21/2017
The vulnerability identified as CVE-2015-0605 resides within the uuencode inspection engine of Cisco AsyncOS operating on Cisco Email Security Appliance devices version 8.5 and earlier. This security flaw represents a critical bypass issue that undermines the intended content filtering mechanisms designed to protect email environments from malicious attachments. The vulnerability specifically affects the email security appliance's ability to properly inspect and block suspicious content when uuencoded attachments are processed through the system.
The technical implementation of this vulnerability stems from insufficient validation within the uuencode inspection engine. When email messages containing crafted uuencoded attachments are processed by the ESA, the system fails to properly decode and analyze the content before applying security policies. This allows attackers to craft malicious payloads that appear benign to the inspection engine while containing hidden malicious code or content that should have been blocked. The flaw enables attackers to circumvent content restrictions that are typically enforced by the email security appliance's policy enforcement mechanisms.
The operational impact of this vulnerability is severe for organizations relying on Cisco ESA for email security. Attackers can exploit this weakness to deliver malicious attachments that would normally be blocked by the system's content filtering rules, potentially leading to successful phishing campaigns, malware delivery, or other malicious activities. The bypass capability means that security policies designed to prevent specific file types or content patterns become ineffective, creating a significant attack surface that can be leveraged for advanced persistent threats. Organizations may experience data breaches or compromise of email systems when this vulnerability is exploited in the wild.
Mitigation strategies for CVE-2015-0605 involve immediate deployment of Cisco's official security patches and updates for the affected ESA versions. Organizations should also implement additional monitoring and logging of email traffic to detect anomalous uuencode patterns that might indicate exploitation attempts. Network administrators should consider implementing additional email security layers beyond the native ESA capabilities, including third-party content inspection tools and enhanced sandboxing solutions. The vulnerability aligns with CWE-20, which addresses "Improper Input Validation," and can be mapped to ATT&CK technique T1193 under "Spearphishing Attachment" where adversaries use encoded attachments to evade detection. Regular security assessments and vulnerability scanning should be conducted to ensure proper patch management and prevent exploitation of similar encoding-based bypass vulnerabilities.