CVE-2000-0196 in Linux
Summary
by MITRE
Buffer overflow in mhshow in the Linux nmh package allows remote attackers to execute commands via malformed MIME headers in an email message.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability identified as CVE-2000-0196 represents a critical buffer overflow flaw within the mhshow utility of the Linux nmh (Network Mail Handler) package. This security issue stems from inadequate input validation mechanisms that fail to properly handle malformed MIME headers in email messages. The mhshow utility serves as a component within the nmh mail handling system that processes and displays email content, making it a potential attack vector for remote command execution.
The technical implementation of this vulnerability occurs when the mhshow utility processes email messages containing specially crafted malformed MIME headers. These headers exceed the allocated buffer space in memory, causing a buffer overflow condition that can be exploited to overwrite adjacent memory locations. The flaw specifically manifests in the handling of email header fields where the application does not properly validate the length of incoming data before copying it into fixed-size buffers. This type of vulnerability falls under the CWE-121 buffer overflow category, which is classified as a common weakness in software design that allows attackers to overwrite memory and potentially execute arbitrary code.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it enables remote attackers to execute arbitrary commands on systems running vulnerable versions of the nmh package. Attackers can craft malicious email messages with oversized MIME headers that trigger the buffer overflow, potentially allowing them to gain unauthorized access to the affected system. The attack vector operates over standard email protocols, making it particularly dangerous as it can be delivered through normal email channels without requiring special privileges or direct system access. This vulnerability aligns with ATT&CK technique T1190 for Exploit Public-Facing Application, as it targets a publicly accessible email processing utility that can be exploited through email messages.
Systems at risk include any Linux environment running vulnerable versions of the nmh package where the mhshow utility is accessible to untrusted email sources. The vulnerability is particularly concerning in networked environments where email processing occurs, as it allows attackers to execute commands with the privileges of the user running the mhshow utility. Mitigation strategies should focus on immediate patching of the nmh package to address the buffer overflow issue, implementing email filtering mechanisms to sanitize incoming headers, and restricting access to email processing utilities. Network segmentation and email gateway configurations should also be reviewed to minimize potential attack surfaces, while monitoring systems should be deployed to detect anomalous email processing patterns that might indicate exploitation attempts.