CVE-2000-0736 in Becky Internet Mail
Summary
by MITRE
Buffer overflow in Becky! Internet Mail client 1.26.04 and earlier allows remote attackers to cause a denial of service via a long Content-type: MIME header when the user forwards a message.
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Analysis
by VulDB Data Team • 04/06/2019
The vulnerability identified as CVE-2000-0736 represents a critical buffer overflow flaw within the Becky! Internet Mail client version 1.26.04 and earlier implementations. This security weakness specifically manifests when the email client processes a forwarded message containing an excessively long Content-type MIME header field. The buffer overflow occurs during the parsing and handling of this particular header field, creating a scenario where maliciously crafted email content can trigger unexpected behavior in the application's memory management. The vulnerability exists at the application layer of the network stack, specifically affecting email client software that fails to properly validate input length before processing MIME headers.
The technical exploitation of this vulnerability relies on the client application's insufficient bounds checking mechanisms when processing email headers. When a user receives and forwards a message containing a Content-type header that exceeds the allocated buffer space, the application's memory management routines become compromised. This overflow condition can overwrite adjacent memory locations, potentially leading to application crashes or, in more sophisticated attack scenarios, arbitrary code execution. The vulnerability is classified as a classic stack-based buffer overflow according to CWE-121, which specifically addresses conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The attack vector requires remote delivery of malicious email content and user interaction through the forwarding process, making it particularly concerning for email client security.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it represents a potential pathway for more severe security breaches within email client environments. When exploited successfully, the buffer overflow can cause the Becky! Internet Mail client to crash and terminate unexpectedly, disrupting user communication and potentially creating a persistent denial of service condition. System administrators and end users who rely on this email client for business communications face significant operational risks, as the vulnerability can be triggered without requiring any special privileges or authentication. The attack scenario requires minimal user interaction, making it particularly dangerous in enterprise environments where email clients are frequently used and forwarded. According to ATT&CK framework, this vulnerability maps to T1203 - Exploitation for Client Execution, as it leverages client-side applications to achieve its malicious objectives.
Mitigation strategies for CVE-2000-0736 should prioritize immediate software updates and patches from the vendor, as the vulnerability affects legacy versions of the Becky! Internet Mail client. Organizations should implement email filtering solutions that can identify and block malformed MIME headers before they reach end-user clients. Network administrators should consider implementing email gateway security measures that sanitize incoming email content, particularly focusing on header field validation and length restrictions. Additionally, user education programs should emphasize the importance of not forwarding suspicious or unexpected email messages. The recommended long-term solution involves migrating to more modern email client implementations that have robust input validation and memory protection mechanisms. Security teams should also implement monitoring solutions to detect unusual application behavior that might indicate exploitation attempts. The vulnerability serves as a critical reminder of the importance of input validation and buffer management in client-side applications, particularly those handling untrusted network data. Organizations should also consider implementing application whitelisting policies to prevent execution of unpatched versions of vulnerable software, thereby reducing the attack surface for similar vulnerabilities.