CVE-2013-1762 in stunnel
Summary
by MITRE
stunnel 4.21 through 4.54, when CONNECT protocol negotiation and NTLM authentication are enabled, does not correctly perform integer conversion, which allows remote proxy servers to execute arbitrary code via a crafted request that triggers a buffer overflow.
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Analysis
by VulDB Data Team • 12/27/2024
The vulnerability identified as CVE-2013-1762 represents a critical buffer overflow condition within stunnel versions ranging from 4.21 through 4.54. This flaw specifically manifests when the application operates with both CONNECT protocol negotiation and NTLM authentication enabled, creating a dangerous combination that exploits integer conversion errors. The vulnerability falls under the category of software security flaws that can lead to arbitrary code execution, making it particularly dangerous for systems that rely on stunnel for secure communications.
The technical implementation of this vulnerability stems from improper handling of integer conversions during the processing of crafted requests. When stunnel receives a request that triggers the CONNECT protocol negotiation combined with NTLM authentication, the application fails to properly validate or convert integer values before using them in buffer allocation calculations. This oversight creates a scenario where an attacker can manipulate the integer values to cause buffer overflows, allowing them to overwrite adjacent memory locations with malicious code. The flaw is classified as a buffer overflow under CWE-121, which specifically addresses heap-based buffer overflow conditions that occur when insufficient space is allocated for data.
The operational impact of this vulnerability extends beyond simple remote code execution, as it provides attackers with the capability to completely compromise systems that utilize vulnerable stunnel configurations. When exploited, the vulnerability enables attackers to execute arbitrary code with the privileges of the stunnel process, which typically runs with elevated permissions. This can result in complete system compromise, data exfiltration, and the establishment of persistent backdoors. The vulnerability is particularly concerning in enterprise environments where stunnel is commonly used as a SSL/TLS proxy server, as it can be leveraged to bypass security controls and gain unauthorized access to sensitive network resources.
The exploitation of CVE-2013-1762 aligns with techniques documented in the MITRE ATT&CK framework under the Tactic of Execution and Persistence. Attackers can leverage this vulnerability to establish initial access through the proxy server and then maintain persistence by installing backdoors or modifying system configurations. The vulnerability also relates to the Defense Evasion category as it can be used to bypass network security controls that rely on stunnel for secure communications. Organizations using stunnel in their infrastructure should immediately implement mitigations including upgrading to patched versions, disabling unnecessary authentication protocols, and implementing network segmentation to limit the potential impact of successful exploitation attempts.
The remediation approach for this vulnerability requires immediate deployment of stunnel patches that address the integer conversion errors and buffer overflow conditions. Organizations should also consider implementing network monitoring to detect unusual CONNECT protocol usage patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and integer handling in security-critical applications, reinforcing industry best practices outlined in standards such as the OWASP Top Ten and NIST cybersecurity guidelines. Additionally, system administrators should conduct comprehensive vulnerability assessments to identify other potentially affected applications and ensure that all proxy server configurations properly validate and sanitize input parameters before processing them.