CVE-1999-0439 in Procmail
Summary
by MITRE
Buffer overflow in procmail before version 3.12 allows remote or local attackers to execute commands via expansions in the procmailrc configuration file.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0439 represents a critical buffer overflow flaw within procmail version 3.12 and earlier, which can be exploited by both remote and local attackers to execute arbitrary commands. This issue stems from improper handling of input data within the procmail configuration file processing mechanism, specifically when dealing with variable expansions. The flaw occurs during the parsing of the .procmailrc file where user-supplied data is not adequately validated or sanitized before being processed, creating an opportunity for malicious input to overflow buffer boundaries and potentially overwrite adjacent memory regions.
The technical implementation of this vulnerability involves the exploitation of unsafe string handling practices within procmail's configuration parser. When procmail encounters variable expansions within the .procmailrc file, it performs string operations that do not properly check buffer boundaries. This allows an attacker to craft malicious input that, when processed, causes a buffer overflow condition. The overflow can be manipulated to overwrite return addresses on the stack or other critical memory locations, enabling attackers to redirect program execution flow. This type of vulnerability is categorized under CWE-121, which describes heap-based buffer overflow conditions, and also aligns with CWE-122, heap-based buffer overflow, as the exploitation can occur through manipulation of heap-allocated memory regions during configuration processing.
The operational impact of this vulnerability extends beyond simple command execution, as it can provide attackers with full system compromise capabilities. Local attackers can leverage this vulnerability to escalate privileges and gain persistent access to systems running vulnerable versions of procmail, while remote attackers can exploit it through mail server configurations or when procmail is used in networked environments. The implications are particularly severe in multi-user environments where procmail is commonly used for mail processing, as it can allow unauthorized users to execute commands with the privileges of the procmail process, potentially leading to complete system compromise.
Security professionals should prioritize immediate remediation through patching or upgrading to procmail version 3.12 or later, which contains fixes for this buffer overflow vulnerability. Additional mitigations include implementing strict input validation for .procmailrc configuration files, restricting write permissions on these files, and employing privilege separation techniques where procmail runs with minimal necessary privileges. Organizations should also consider implementing intrusion detection systems to monitor for suspicious patterns in mail processing activities and establish comprehensive monitoring protocols for any unauthorized modifications to mail configuration files. The vulnerability's classification under attack techniques such as T1059 in the MITRE ATT&CK framework highlights its potential for command execution and privilege escalation, making it a critical target for immediate security remediation efforts.