CVE-2003-0966 in ELM
Summary
by MITRE
Buffer overflow in the frm command in elm 2.5.6 and earlier, and possibly later versions, allows remote attackers to execute arbitrary code via a long Subject line.
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Analysis
by VulDB Data Team • 06/29/2021
The vulnerability identified as CVE-2003-0966 represents a critical buffer overflow flaw affecting the elm email client software version 2.5.6 and earlier, with potential impacts extending to subsequent releases. This vulnerability resides within the frm command implementation where the software fails to properly validate input length when processing email Subject lines. The buffer overflow occurs when an attacker crafts a maliciously long Subject header that exceeds the allocated buffer space, causing adjacent memory to be overwritten with attacker-controlled data.
The technical nature of this vulnerability aligns with CWE-121, which categorizes buffer overflow conditions where insufficient bounds checking allows data to be written beyond the allocated buffer boundaries. The flaw specifically manifests in the email parsing routine where the frm command processes incoming email headers without adequate input sanitization. When the Subject line exceeds the predetermined buffer limit, the overflow can overwrite return addresses, function pointers, or other critical program state information in the stack memory. This memory corruption directly enables attackers to manipulate program execution flow and potentially inject malicious code that executes with the privileges of the affected process.
From an operational perspective, this vulnerability presents a significant risk to email server and client systems that utilize the elm email client. Attackers can exploit this weakness remotely by sending specially crafted emails containing excessively long Subject lines to vulnerable systems. The remote execution capability means that compromised systems could be exploited without requiring local access or user interaction beyond receiving the malicious email. The impact extends beyond simple code execution to potential system compromise, data theft, or use as a stepping stone for further network penetration attacks. This vulnerability particularly affects environments where elm is used as a mail transfer agent or client software, making it relevant to enterprise email infrastructure and desktop email clients.
The exploitation of this vulnerability can be mapped to several ATT&CK techniques including T1059 for command and scripting interpreter usage, T1068 for exploit for privilege escalation, and T1133 for external remote services. Organizations should implement immediate mitigations including patching to versions of elm that address the buffer overflow issue, implementing email header length restrictions at network boundaries, and deploying intrusion detection systems that can identify suspicious email patterns. Network administrators should also consider implementing email filtering rules that limit the length of Subject headers or block emails from known malicious sources. Additionally, system hardening measures such as stack canaries, address space layout randomization, and non-executable stack protections can provide additional defense-in-depth layers against exploitation attempts. The vulnerability underscores the importance of regular security updates and input validation practices in preventing remote code execution exploits in email processing software.