CVE-2002-0002 in Stunnel
Summary
by MITRE
Format string vulnerability in stunnel before 3.22 when used in client mode for (1) smtp, (2) pop, or (3) nntp allows remote malicious servers to execute arbitrary code.
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Analysis
by VulDB Data Team • 12/16/2024
The vulnerability described in CVE-2002-0002 represents a critical format string vulnerability within the stunnel software ecosystem, specifically affecting versions prior to 3.22 when operating in client mode. This flaw manifests in the handling of network protocols including smtp, pop, and nntp, creating a significant security risk for systems that rely on stunnel for secure communications. The vulnerability stems from improper input validation and handling of format specifiers within the application's string processing functions, allowing malicious remote servers to manipulate the format string parsing mechanism.
The technical implementation of this vulnerability involves the exploitation of unsafe string formatting functions such as printf, sprintf, or related variants that do not properly validate user-supplied input before processing. When stunnel operates in client mode and connects to malicious servers responding with crafted format specifiers, the application's failure to sanitize these inputs enables attackers to inject malicious format specifiers that can lead to memory corruption and arbitrary code execution. This type of vulnerability falls under the CWE-134 category of "Use of Externally-Controlled Format String," which is classified as a high-severity weakness in the Common Weakness Enumeration catalog. The attack vector specifically targets the client-side processing of network responses, where the application expects to receive legitimate protocol data but instead encounters maliciously crafted format strings.
The operational impact of this vulnerability extends beyond simple privilege escalation or denial of service scenarios, as it provides attackers with full arbitrary code execution capabilities on systems running vulnerable versions of stunnel. This means that compromised systems could be used as launch points for further attacks within network environments, potentially leading to complete system compromise. The vulnerability affects organizations that use stunnel for secure email communications through smtp, pop, and nntp protocols, making it particularly dangerous for enterprises relying on these communication channels. According to ATT&CK framework, this vulnerability maps to T1059.007 for Command and Scripting Interpreter and T1566.001 for Phishing, as it enables attackers to execute malicious code remotely and potentially establish persistent access through compromised communication channels. The vulnerability also aligns with T1190 for Exploit Public-Facing Application, as it represents an exploitable weakness in a widely-used network security tool.
Mitigation strategies for CVE-2002-0002 require immediate patching of stunnel installations to version 3.22 or later, which includes proper input sanitization and format string handling mechanisms. Organizations should also implement network segmentation and monitoring to detect suspicious protocol traffic patterns that might indicate exploitation attempts. Additional protective measures include disabling unnecessary protocol support in stunnel configurations, implementing strict certificate validation procedures, and conducting regular security assessments of network services. The vulnerability serves as a critical reminder of the importance of proper input validation in security-critical applications and demonstrates how seemingly minor implementation flaws can result in severe privilege escalation capabilities. Security teams should also consider implementing intrusion detection systems capable of identifying format string exploitation attempts and establish incident response procedures specifically addressing this class of vulnerability.