CVE-2004-0399 in Internet Mailer
Summary
by MITRE
Stack-based buffer overflow in Exim 3.35, and other versions before 4, when the sender_verify option is true, allows remote attackers to cause a denial of service and possibly execute arbitrary code during sender verification.
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Analysis
by VulDB Data Team • 12/20/2024
The vulnerability described in CVE-2004-0399 represents a critical stack-based buffer overflow flaw affecting Exim email server versions 3.35 and earlier, specifically when the sender_verify option is enabled. This vulnerability resides in the sender verification functionality that Exim employs to validate sender addresses during message processing. The flaw occurs when the mail server processes sender addresses that exceed the allocated buffer size, creating an exploitable condition that can be leveraged by remote attackers to compromise system integrity.
The technical implementation of this vulnerability stems from inadequate input validation within the sender verification mechanism. When sender_verify is enabled, Exim performs checks on sender addresses to verify their legitimacy, but fails to properly enforce buffer boundaries during string processing operations. This allows attackers to craft malicious sender addresses containing excessive data that overflows the allocated stack buffer, potentially corrupting adjacent memory locations and overwriting critical program execution data. The vulnerability specifically targets the stack memory region where local variables and return addresses are stored, making it particularly dangerous for exploitation purposes.
From an operational perspective, this vulnerability presents a significant risk to email server infrastructure as it can be exploited remotely without authentication requirements. Attackers can trigger the buffer overflow by sending specially crafted emails with malicious sender addresses, potentially leading to denial of service conditions that render the mail server unavailable to legitimate users. More critically, successful exploitation can result in arbitrary code execution with the privileges of the Exim process, which typically runs with elevated system permissions. This capability enables attackers to gain unauthorized access to the underlying system, potentially escalating privileges and establishing persistent access to the network infrastructure.
The impact of this vulnerability extends beyond simple service disruption as it provides a pathway for complete system compromise through the exploitation of the stack-based buffer overflow. The attacker-controlled input flows directly into the vulnerable code path during sender verification, creating a direct attack vector that bypasses traditional authentication mechanisms. This vulnerability aligns with CWE-121, which categorizes stack-based buffer overflow conditions, and represents a classic example of how improper input validation can lead to memory corruption exploits. The attack surface is particularly concerning given that many organizations rely on Exim for email services, making this vulnerability a prime target for widespread exploitation.
Security mitigations for CVE-2004-0399 require immediate implementation of the official Exim security patches released by the vendor, which address the buffer overflow through proper input validation and bounds checking mechanisms. Organizations should disable the sender_verify option if it is not strictly required for their email infrastructure, as this eliminates the vulnerable code path entirely. Additionally, implementing network-level controls such as email filtering rules and monitoring for suspicious sender address patterns can provide additional defense-in-depth measures. The vulnerability demonstrates the importance of regular security updates and the need for proper input validation in network services, aligning with ATT&CK technique T1203 which covers the exploitation of software vulnerabilities for privilege escalation and system compromise. System administrators should also consider implementing intrusion detection systems to monitor for exploitation attempts and maintain comprehensive audit logs to track potential compromise indicators.