CVE-2005-0022 in Internet Mailer
Summary
by MITRE
Buffer overflow in the spa_base64_to_bits function in Exim before 4.43, as originally obtained from Samba code, and as called by the auth_spa_client function, may allow attackers to execute arbitrary code during SPA authentication.
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Analysis
by VulDB Data Team • 06/30/2019
The vulnerability identified as CVE-2005-0022 represents a critical buffer overflow condition within the Exim mail transfer agent that existed in versions prior to 4.43. This flaw was inherited from Samba code and specifically manifested within the spa_base64_to_bits function, which served as a crucial component in the Single Password Authentication (SPA) mechanism. The vulnerability emerged from the improper handling of base64 encoded data during authentication processes, creating a pathway for malicious actors to exploit the system through carefully crafted input sequences.
The technical implementation of this vulnerability stems from inadequate bounds checking within the spa_base64_to_bits function, which processes base64 encoded strings during SPA authentication. When the auth_spa_client function invoked this vulnerable subroutine, it passed base64 encoded authentication data without sufficient validation of input length or buffer boundaries. This deficiency allowed attackers to supply maliciously formatted base64 strings that would exceed the allocated buffer space, resulting in memory corruption that could be leveraged to execute arbitrary code with the privileges of the Exim process. The vulnerability aligns with CWE-121, which categorizes buffer overflow conditions where insufficient bounds checking permits data to overwrite adjacent memory locations.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a direct pathway to compromise mail servers running vulnerable versions of Exim. During SPA authentication, when legitimate users or malicious actors submit authentication credentials, the system processes these inputs through the flawed spa_base64_to_bits function. The buffer overflow condition creates an exploitable memory corruption scenario that can be manipulated to overwrite critical program execution flow, potentially allowing remote code execution. This represents a significant threat to email infrastructure security, particularly in environments where Exim serves as the primary mail transfer agent and SPA authentication is configured.
Security practitioners should note that this vulnerability demonstrates the importance of code auditing when integrating third-party components, as the flaw originated from Samba code that was incorporated into Exim without adequate security review. The exploitation of this vulnerability aligns with ATT&CK technique T1059, which covers command and scripting interpreter usage, as successful exploitation would likely involve executing malicious code within the target system context. Organizations should prioritize immediate patching of Exim installations to version 4.43 or later, as this release contains the necessary fixes to address the buffer overflow condition. Additionally, network monitoring should be implemented to detect anomalous authentication patterns that might indicate exploitation attempts, while access controls should be reviewed to minimize potential impact should exploitation occur. The vulnerability serves as a reminder of the critical importance of input validation and proper memory management in security-sensitive applications, particularly those handling authentication mechanisms where input validation failures can lead to complete system compromise.