CVE-2001-0889 in Exim
Summary
by MITRE
Exim 3.22 and earlier, in some configurations, does not properly verify the local part of an address when redirecting the address to a pipe, which could allow remote attackers to execute arbitrary commands via shell metacharacters.
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Analysis
by VulDB Data Team • 10/01/2025
The vulnerability identified as CVE-2001-0889 represents a critical command injection flaw in Exim email transfer agents version 3.22 and earlier. This issue specifically affects systems where Exim is configured to redirect email addresses to external pipes or command execution mechanisms. The flaw stems from inadequate input validation during the address parsing process, particularly concerning the local part of email addresses that precedes the @ symbol. When Exim processes email redirections to pipes, it fails to properly sanitize or escape special shell metacharacters contained within the local address portion, creating a pathway for malicious actors to inject arbitrary commands.
The technical nature of this vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in shell commands, and CWE-94, which covers improper control of generation of code. The flaw operates at the intersection of email processing and shell command execution, where the mail transfer agent's insufficient sanitization allows attackers to manipulate the command execution flow. When an attacker crafts a malicious email address containing shell metacharacters such as semicolons, ampersands, or backticks within the local part, these characters can be interpreted by the underlying shell during pipe execution, leading to unauthorized command execution on the affected system.
From an operational impact perspective, this vulnerability enables remote attackers to execute arbitrary commands with the privileges of the Exim process, typically running as the mail user or root depending on system configuration. The attack surface extends to any system running vulnerable Exim versions that have email redirections configured to pipe messages to external commands or scripts. This creates potential for complete system compromise, data exfiltration, privilege escalation, and persistent backdoor establishment. The vulnerability is particularly dangerous because it requires no authentication for exploitation, making it a significant threat to email server security.
The attack vector for CVE-2001-0889 leverages the fundamental design flaw in Exim's address handling mechanism, where the system fails to implement proper input validation before passing address components to shell execution contexts. Attackers can exploit this by sending specially crafted emails to addresses that are configured for pipe redirection, thereby triggering the vulnerable code path. This vulnerability also maps to ATT&CK technique T1059.001, which covers command and scripting interpreter execution, and T1068, which deals with local privilege escalation. The remediation strategy involves immediate patching of Exim to version 3.23 or later, which includes proper input sanitization for address components. Additionally, system administrators should review and restrict pipe redirection configurations, implement proper input validation for email addresses, and consider implementing email filtering mechanisms to prevent malicious address patterns from reaching vulnerable systems. Network segmentation and monitoring for unusual command execution patterns can also serve as supplementary defensive measures against exploitation attempts.