CVE-2001-0690 in Exim
Summary
by MITRE
Format string vulnerability in exim (3.22-10 in Red Hat, 3.12 in Debian and 3.16 in Conectiva) in batched SMTP mode allows a remote attacker to execute arbitrary code via format strings in SMTP mail headers.
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Analysis
by VulDB Data Team • 10/07/2024
The vulnerability identified as CVE-2001-0690 represents a critical format string flaw in the exim mail transfer agent version 3.22-10 distributed by Red Hat, with similar issues present in Debian 3.12 and Conectiva 3.16 releases. This vulnerability specifically manifests in batched SMTP mode where the mail server processes multiple messages simultaneously, creating a unique attack surface that differs from standard SMTP operations. The flaw stems from improper input validation within the SMTP header processing routines where the application directly uses user-supplied data without proper sanitization or formatting controls.
The technical implementation of this vulnerability occurs when exim processes SMTP mail headers containing format specifiers such as %s, %d, or %x within the batched SMTP processing context. When these unvalidated format strings are passed to functions like printf or sprintf without proper formatting parameters, the application's memory layout becomes exploitable. Attackers can craft malicious SMTP headers that contain crafted format specifiers designed to read arbitrary memory locations, overwrite critical program variables, or even inject and execute malicious code within the mail server's execution context. This type of vulnerability falls under CWE-134 which specifically addresses the use of format strings inappropriately, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter.
The operational impact of this vulnerability extends beyond simple code execution as it provides attackers with complete control over the mail server's operations. Successful exploitation can lead to unauthorized access to email communications, potential data exfiltration, server compromise, and subsequent lateral movement within the network infrastructure. The batched SMTP mode creates additional complexity because multiple simultaneous connections can be exploited, potentially allowing for more sophisticated attack vectors and increased payload delivery capabilities. The vulnerability affects organizations heavily dependent on email services and could result in significant service disruption, data breaches, and compliance violations.
Mitigation strategies for CVE-2001-0690 require immediate patching of the exim mail server to versions that properly validate and sanitize all SMTP header inputs before processing. Organizations should implement network-level controls such as SMTP filtering rules that can identify and block suspicious format string patterns in email headers. The principle of least privilege should be enforced by running exim with minimal required permissions and implementing strict input validation at all network boundaries. Additionally, monitoring systems should be configured to detect unusual SMTP header patterns and potential exploitation attempts. Security teams should also consider implementing email content filtering solutions that can identify and quarantine messages containing potentially malicious format strings. The vulnerability highlights the importance of proper input validation and the dangers of using user-controlled data in format string functions, making it a prime example of why secure coding practices and regular security audits are essential for maintaining system integrity.