CVE-2001-0692 in Firebox 2500
Summary
by MITRE
SMTP proxy in WatchGuard Firebox (2500 and 4500) 4.5 and 4.6 allows a remote attacker to bypass firewall filtering via a base64 MIME encoded email attachment whose boundary name ends in two dashes.
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Analysis
by VulDB Data Team • 07/09/2014
The vulnerability identified as CVE-2001-0692 affects the SMTP proxy functionality within WatchGuard Firebox 2500 and 4500 series devices running firmware versions 4.5 and 4.6. This security flaw resides in the email filtering mechanisms that process incoming and outgoing SMTP traffic through the firewall appliance. The issue specifically manifests in how the system handles base64 encoded MIME email attachments, creating a potential pathway for malicious actors to circumvent the intended security controls. The vulnerability operates at the application layer of the network stack, targeting the email proxy service that is responsible for inspecting and filtering email content before allowing it to pass through the firewall.
The technical exploitation of this vulnerability stems from a specific parsing error in the MIME boundary handling mechanism within the SMTP proxy. When processing base64 encoded email attachments, the system fails to properly validate or sanitize boundary names that end with two consecutive dashes. This improper boundary validation allows an attacker to craft malicious email messages where the boundary delimiter sequence terminates with double dashes, effectively confusing the email parsing logic. The flaw operates under CWE-129, which encompasses issues related to improper validation of input boundaries, and can be categorized as a buffer over-read or boundary condition error. The vulnerability essentially allows an attacker to manipulate the MIME parsing process to bypass content filtering rules that would normally prevent certain types of attachments from traversing the firewall.
The operational impact of this vulnerability extends beyond simple bypass of firewall rules, as it can enable attackers to deliver malicious payloads through email channels that would otherwise be blocked by security policies. An attacker could potentially send malware attachments, phishing content, or other malicious materials that would normally be rejected by the email filtering system. This creates a significant risk for organizations relying on WatchGuard Firebox appliances for email security, as the vulnerability essentially creates a backdoor for content that should be blocked by the firewall's email filtering capabilities. The attack vector requires remote access and does not necessitate physical presence or elevated privileges, making it particularly dangerous for enterprise environments where email is a primary communication channel. The vulnerability can be exploited through standard SMTP traffic without requiring specialized tools or techniques, increasing its potential for widespread exploitation.
Organizations affected by this vulnerability should immediately implement mitigations including firmware upgrades to versions that address the boundary parsing issue, as well as temporary network segmentation strategies to limit email traffic exposure. The implementation of additional email filtering layers outside the WatchGuard appliance can provide defense in depth. Network administrators should also consider implementing stricter email content filtering policies and monitoring for unusual email boundary patterns. From an ATT&CK framework perspective, this vulnerability maps to technique T1190 for exploit for lateral movement through email-based attacks, and T1078 for valid accounts for persistence. The vulnerability demonstrates a classic case of insufficient input validation in network security appliances and highlights the importance of proper MIME parsing implementation in email security systems. Organizations should also review their incident response procedures to ensure rapid identification and containment of potential exploitation attempts, particularly focusing on email traffic monitoring and anomaly detection for unusual boundary patterns in MIME content.