CVE-2010-4344 in Exim
Summary
by MITRE
Heap-based buffer overflow in the string_vformat function in string.c in Exim before 4.70 allows remote attackers to execute arbitrary code via an SMTP session that includes two MAIL commands in conjunction with a large message containing crafted headers, leading to improper rejection logging.
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Analysis
by VulDB Data Team • 04/22/2026
The vulnerability identified as CVE-2010-4344 represents a critical heap-based buffer overflow within the Exim mail transfer agent software. This flaw exists in the string_vformat function located in the string.c source file and affects Exim versions prior to 4.70. The vulnerability arises during SMTP session processing when an attacker crafts a specific sequence of commands that triggers the buffer overflow condition. The attack vector involves sending two MAIL commands followed by a large message containing carefully constructed headers, which causes the software to improperly handle logging operations and subsequently execute arbitrary code on the affected system. This represents a sophisticated exploit that leverages the interaction between SMTP command processing and internal logging mechanisms to achieve remote code execution.
The technical nature of this vulnerability stems from improper bounds checking within the string_vformat function, which is responsible for formatting strings during message processing. When the function processes the crafted headers in conjunction with the double MAIL commands, it fails to properly validate the length of input data before copying it into fixed-size heap buffers. This classic buffer overflow condition allows attackers to overwrite adjacent memory locations, potentially corrupting program execution flow and enabling arbitrary code execution. The vulnerability operates at the intersection of network protocol handling and memory management, making it particularly dangerous as it can be exploited through standard SMTP communication channels without requiring authentication or privileged access. The flaw specifically relates to CWE-121 Heap-based Buffer Overflow, which is categorized under the broader class of memory safety issues in software development.
The operational impact of CVE-2010-4344 is severe and multifaceted, as it enables remote code execution on systems running vulnerable versions of Exim. An attacker who successfully exploits this vulnerability can gain complete control over the affected mail server, potentially using it as a launching point for further attacks within the network infrastructure. The vulnerability's exploitation requires minimal privileges and can be executed through standard SMTP traffic, making it particularly attractive to threat actors. Organizations relying on Exim for email services face significant risk of data breaches, service disruption, and potential lateral movement within their networks. The improper rejection logging aspect of the vulnerability means that administrators may not even be aware of successful exploitation attempts, as the system may appear to function normally while malicious code executes in the background. This characteristic aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1566 for Phishing, as the compromised server could be used for further malicious activities.
Mitigation strategies for CVE-2010-4344 primarily focus on immediate software updates and system hardening measures. The most effective remediation is upgrading to Exim version 4.70 or later, which contains patches addressing the buffer overflow condition in the string_vformat function. Organizations should also implement network-level restrictions to limit SMTP access to trusted sources and deploy intrusion detection systems capable of identifying suspicious SMTP traffic patterns. Additional defensive measures include implementing proper input validation for email headers, configuring rate limiting for SMTP commands, and establishing comprehensive monitoring for unauthorized access attempts. System administrators should also consider deploying sandboxing techniques and privilege separation to limit the potential impact of successful exploitation. The vulnerability demonstrates the importance of maintaining up-to-date security patches and implementing defense-in-depth strategies to protect critical infrastructure components such as mail servers that handle sensitive communications.