CVE-2019-10149 in Exim
Summary
by MITRE
A flaw was found in Exim versions 4.87 to 4.91 (inclusive). Improper validation of recipient address in deliver_message() function in /src/deliver.c may lead to remote command execution.
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Analysis
by VulDB Data Team • 04/01/2025
The vulnerability identified as CVE-2019-10149 represents a critical remote code execution flaw within the Exim mail transfer agent that affects versions 4.87 through 4.91. This issue resides in the deliver_message() function located in the /src/deliver.c source file, where inadequate validation of recipient addresses creates a pathway for malicious actors to execute arbitrary commands on affected systems. The flaw stems from insufficient input sanitization when processing email recipient addresses, allowing crafted malicious inputs to bypass normal validation checks and potentially trigger unintended system behavior.
The technical implementation of this vulnerability involves the improper handling of recipient address parsing within Exim's delivery mechanism. When the mail system processes incoming messages, the deliver_message() function fails to adequately validate the format and content of recipient addresses, particularly those containing special characters or sequences that could be interpreted as command invocations. This validation gap enables attackers to inject malicious payloads through carefully constructed recipient addresses that are then processed without proper sanitization, leading to command execution with the privileges of the Exim process. The vulnerability operates at the application layer and can be exploited through standard email transmission protocols without requiring authentication or special privileges.
The operational impact of CVE-2019-10149 extends beyond simple remote code execution, as it can enable full system compromise when exploited successfully. An attacker who can send emails to an affected Exim server can potentially gain complete control over the host system, including the ability to execute arbitrary commands, access sensitive data, establish persistence mechanisms, and move laterally within network environments. This vulnerability particularly affects organizations relying on Exim for email services, as it provides an attack vector that can be exploited through standard email traffic without requiring additional reconnaissance or privilege escalation. The widespread adoption of Exim across various operating systems and server configurations amplifies the potential impact of this vulnerability.
Security mitigations for CVE-2019-10149 primarily involve immediate patching of affected Exim installations to versions that contain the necessary validation fixes. Organizations should prioritize updating their Exim servers to versions 4.92 or later, which contain the corrected deliver_message() function implementation that properly validates recipient addresses. Additionally, network-level protections such as email filtering rules, rate limiting, and monitoring for unusual recipient address patterns can provide additional defense-in-depth measures. The vulnerability aligns with CWE-20 Improper Input Validation, and its exploitation patterns correspond to ATT&CK techniques including T1059 Command and Scripting Interpreter and T1078 Valid Accounts for maintaining persistent access. Organizations should also implement proper logging and monitoring of email delivery processes to detect potential exploitation attempts and ensure that system administrators regularly review security updates and apply patches according to established security protocols.