CVE-1999-0940 in Mutt
Summary
by MITRE
Buffer overflow in mutt mail client allows remote attackers to execute commands via malformed MIME messages.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0940 represents a critical buffer overflow flaw within the mutt mail client software that was first documented in 1999. This issue stems from inadequate input validation mechanisms within the email client's handling of MIME (Multipurpose Internet Mail Extensions) message formats. The mutt client, which was widely used as a console-based email reader, failed to properly validate the length of data fields within MIME attachments, creating a scenario where maliciously crafted email messages could trigger memory corruption. The flaw specifically manifests when the client processes malformed MIME content that exceeds predetermined buffer limits, leading to potential memory overwrite conditions that could be exploited by remote attackers. This vulnerability operates at the application layer and affects systems where mutt is installed and configured to process incoming email messages containing crafted MIME structures. The buffer overflow vulnerability falls under CWE-121, which categorizes buffer overflow conditions that occur when a program writes data beyond the boundaries of a fixed-length buffer. The technical implementation of this flaw demonstrates how improper bounds checking in string manipulation operations can create exploitable conditions that allow attackers to overwrite adjacent memory locations, potentially including return addresses or function pointers.
The operational impact of CVE-1999-0940 extends beyond simple denial of service scenarios, as it provides remote attackers with the capability to execute arbitrary code on vulnerable systems. When a user opens an email containing a specially crafted MIME message, the mutt client's buffer overflow condition can be triggered, allowing an attacker to inject and execute malicious code with the privileges of the user running the email client. This exploitation scenario typically involves crafting a malicious email with oversized MIME headers or content that forces the application to write beyond allocated memory boundaries. The attack vector is particularly dangerous because it requires no special privileges from the end user and can be delivered through standard email channels. The vulnerability affects systems where mutt is installed and actively processes email messages, making it a significant concern for organizations relying on console-based email clients. The potential for remote code execution creates a substantial risk for both individual users and enterprise environments where email clients are used to process messages from untrusted sources.
Mitigation strategies for CVE-1999-0940 should focus on immediate patching of affected mutt versions, as this vulnerability was addressed through software updates that implemented proper bounds checking for MIME message parsing. Organizations should also implement email filtering mechanisms that can identify and quarantine suspicious MIME structures before they reach end-user mail clients. Network-level security controls such as email gateway filtering can help prevent malformed MIME content from entering the email infrastructure. Additionally, system administrators should consider implementing privilege separation techniques where email clients run with reduced privileges to limit the potential impact of successful exploitation attempts. The vulnerability demonstrates the importance of proper input validation and memory management practices in software development, aligning with ATT&CK technique T1059.007 which covers command and scripting interpreter usage. Security monitoring should include detection of unusual memory access patterns and potential buffer overflow indicators in email processing logs. Organizations should also maintain updated threat intelligence regarding similar vulnerabilities in email client software and ensure that all email infrastructure components receive regular security updates and patches. The remediation process should include comprehensive testing of patched versions to ensure that the fix does not introduce regressions in legitimate email processing functionality while effectively addressing the buffer overflow condition.