CVE-2000-0735 in Becky Internet Mail
Summary
by MITRE
Buffer overflow in Becky! Internet Mail client 1.26.03 and earlier allows remote attackers to cause a denial of service via a long Content-type: MIME header when the user replies to a message.
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Analysis
by VulDB Data Team • 05/31/2019
The vulnerability described in CVE-2000-0735 represents a classic buffer overflow flaw within the Becky! Internet Mail client software version 1.26.03 and earlier. This security weakness specifically manifests when the email client processes a malformed MIME header during the reply operation, creating a condition where maliciously crafted email content can trigger unexpected behavior in the application's memory management. The vulnerability exists at the application layer where the client fails to properly validate the length of the Content-type MIME header field, allowing an attacker to supply input that exceeds the allocated buffer space. This particular flaw demonstrates the importance of proper input validation and bounds checking in email client applications that handle untrusted data from external sources.
The technical implementation of this buffer overflow occurs when the Becky! client attempts to parse and process the Content-type header field in an email message. When a user replies to a message containing an excessively long Content-type header, the application's internal buffer allocation mechanism fails to properly handle the oversized input, resulting in memory corruption. The overflow typically occurs in the client's MIME parsing routine where the software attempts to store the header information into a fixed-size buffer without adequate bounds checking. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, where the attacker can manipulate the program's execution flow by overwriting adjacent memory locations. The vulnerability is particularly dangerous because it requires no special privileges or authentication from the attacker, as the exploit can be delivered through standard email communication channels.
The operational impact of this vulnerability extends beyond simple denial of service, though that is the primary effect described in the CVE. When successfully exploited, the buffer overflow causes the Becky! Internet Mail client application to crash or become unresponsive, effectively rendering the email client unusable for the affected user. This denial of service condition can be particularly disruptive in enterprise environments where users rely on specific email clients for business communications. The vulnerability also represents a potential vector for more sophisticated attacks if the attacker can gain control over the application's execution flow through careful manipulation of the overflowed memory regions. From an attack perspective, this vulnerability aligns with the ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage client-side vulnerabilities to compromise user systems. The ease of exploitation through simple email delivery makes this a particularly concerning vulnerability for widespread impact.
Mitigation strategies for CVE-2000-0735 should focus on immediate software updates and patches provided by the vendor, as well as implementing defensive measures at the network level. Users should upgrade to Becky! Internet Mail client versions that have addressed this buffer overflow vulnerability through proper bounds checking and input validation. Network administrators should consider implementing email filtering solutions that can identify and block suspicious MIME headers with excessive lengths before they reach end-user systems. Additionally, organizations should establish regular patch management procedures to ensure all email client software remains up to date with the latest security fixes. The vulnerability underscores the importance of secure coding practices and input validation in email client applications, particularly when processing untrusted data from external sources. Organizations should also consider implementing application whitelisting policies and user education to reduce the risk of exploitation through social engineering vectors that might accompany such email-based attacks.