CVE-2005-0100 in Emacs
Summary
by MITRE
Format string vulnerability in the movemail utility in (1) Emacs 20.x, 21.3, and possibly other versions, and (2) XEmacs 21.4 and earlier, allows remote malicious POP3 servers to execute arbitrary code via crafted packets.
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Analysis
by VulDB Data Team • 06/05/2019
The vulnerability identified as CVE-2005-0100 represents a critical format string flaw within the movemail utility of several prominent text editors including Emacs 20.x, 21.3, and XEmacs 21.4 and earlier versions. This vulnerability stems from improper input validation when processing email headers during POP3 protocol communication, creating a pathway for remote code execution through maliciously crafted server responses. The movemail utility, designed to retrieve and process email messages, fails to properly sanitize format specifiers contained within received email headers, leading to exploitable behavior when these headers are processed through vulnerable printf-style functions.
The technical exploitation of this vulnerability occurs when a malicious POP3 server sends specially crafted email headers containing format specifiers such as %s, %n, or other printf directives. When the movemail utility processes these headers, the format string vulnerability allows attackers to manipulate memory contents and potentially execute arbitrary code with the privileges of the user running the email client. This type of vulnerability maps directly to CWE-134, which specifically addresses the use of format strings in a context where user-supplied data can influence the format string itself. The vulnerability's exploitation mechanism aligns with attack patterns described in the ATT&CK framework under T1059.007 for command and script injection techniques, where adversaries leverage format string vulnerabilities to gain unauthorized code execution.
The operational impact of CVE-2005-0100 extends beyond simple remote code execution to encompass complete system compromise when users interact with malicious email servers. Since movemail is typically invoked automatically during email retrieval processes, users may unknowingly trigger the vulnerability without direct interaction. The vulnerability affects both Emacs and XEmacs installations across multiple versions, creating a substantial attack surface that would have impacted numerous users in 2005 and potentially beyond. The exploitability of this vulnerability requires minimal network interaction, making it particularly dangerous as attackers only need to control a POP3 server to deliver malicious payloads. Organizations using these email clients would have faced significant risk when accessing email from untrusted sources, as the vulnerability could be exploited without user knowledge or consent. The remediation approach involves updating to patched versions of Emacs and XEmacs, with the vulnerability being addressed through proper input sanitization and format string handling mechanisms that prevent user-controllable data from influencing printf function behavior. Security practitioners should also implement network-level protections such as email filtering and monitoring to detect anomalous POP3 traffic patterns that might indicate exploitation attempts, while ensuring that email clients are configured to avoid automatic processing of untrusted email headers.