CVE-2023-42117 in Exim
Summary
by MITRE • 05/03/2024
Exim Improper Neutralization of Special Elements Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of Exim. Authentication is not required to exploit this vulnerability.
The specific flaw exists within the smtp service, which listens on TCP port 25 by default. The issue results from the lack of proper validation of user-supplied data, which can result in a memory corruption condition. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-17554.
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Analysis
by VulDB Data Team • 08/08/2025
The CVE-2023-42117 vulnerability represents a critical remote code execution flaw in the Exim mail transfer agent that has significant implications for email server security. This vulnerability resides within the smtp service component that typically operates on TCP port 25, making it an attractive target for attackers seeking to compromise email infrastructure. The flaw stems from improper neutralization of special elements in user-supplied data, creating a pathway for malicious actors to inject and execute arbitrary code on affected systems. The vulnerability is particularly dangerous because it does not require authentication for exploitation, meaning that any remote attacker can potentially leverage this weakness without prior access credentials. This characteristic places it in the category of severe vulnerabilities that can be exploited at scale, particularly in environments where email servers are exposed to the internet.
The technical nature of this vulnerability involves a memory corruption condition that occurs when the smtp service fails to properly validate incoming data from network connections. This improper validation allows attackers to craft malicious input that can manipulate memory structures within the Exim process, ultimately leading to code execution in the context of the current process. The vulnerability demonstrates characteristics consistent with CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1190 for exploitation of remote services. When an attacker successfully exploits this vulnerability, they can execute code with the privileges of the Exim process, which typically runs with system-level permissions, potentially enabling full system compromise. The memory corruption aspect suggests that the vulnerability may involve stack or heap manipulation through crafted input sequences that overwrite critical memory locations.
The operational impact of CVE-2023-42117 extends beyond simple code execution, as it represents a complete compromise of email server infrastructure. Organizations running affected Exim versions face potential data breaches, as attackers can use this vulnerability to access email content, exfiltrate sensitive information, and establish persistent access points. The vulnerability's accessibility without authentication means that automated exploitation tools could rapidly target exposed email servers, leading to widespread compromise across internet-connected systems. Network administrators must consider the broader implications for their email infrastructure, including potential use as a pivot point for lateral movement within networks and as a staging area for further attacks. The vulnerability affects systems where Exim is configured to accept incoming SMTP connections, making it particularly concerning for organizations that rely on their email servers for business-critical communications and data exchange.
Mitigation strategies for CVE-2023-42117 should prioritize immediate patching of affected Exim installations to address the root cause of the vulnerability. Organizations should implement network segmentation to limit exposure of email servers to external networks and consider blocking incoming connections on TCP port 25 from untrusted sources. Security monitoring should be enhanced to detect unusual patterns in SMTP traffic that might indicate exploitation attempts, including malformed input sequences or unexpected connection behavior. Additionally, organizations should implement proper input validation and sanitization measures for all email-related services, aligning with industry standards for secure coding practices. The vulnerability's classification as a remote code execution flaw necessitates comprehensive incident response planning, including system isolation procedures, forensic analysis capabilities, and recovery protocols. Organizations should also review their email server configurations to ensure that unnecessary services are disabled and that proper access controls are implemented to minimize the attack surface. Regular security assessments and vulnerability scanning should be conducted to identify and remediate similar vulnerabilities in other system components.