CVE-2014-3956 in Sendmail
Summary
by MITRE
The sm_close_on_exec function in conf.c in sendmail before 8.14.9 has arguments in the wrong order, and consequently skips setting expected FD_CLOEXEC flags, which allows local users to access unintended high-numbered file descriptors via a custom mail-delivery program.
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Analysis
by VulDB Data Team • 06/20/2021
The vulnerability identified as CVE-2014-3956 resides within the sendmail mail transfer agent software, specifically in the configuration handling component known as conf.c. This issue affects sendmail versions prior to 8.14.9 and represents a critical flaw in the software's file descriptor management system. The vulnerability stems from a fundamental programming error where the arguments passed to the sm_close_on_exec function are incorrectly ordered, leading to improper handling of file descriptor flags that should control process execution behavior.
The technical flaw manifests when the sm_close_on_exec function receives its parameters in the wrong sequence, causing the system to skip the proper setting of the FD_CLOEXEC flag on file descriptors. This flag is essential for ensuring that file descriptors are automatically closed when a process executes a new program, preventing unintended information leakage between processes. When this flag is not properly set, file descriptors that should be closed remain open and accessible to subsequent processes, creating a significant security risk. The vulnerability specifically impacts high-numbered file descriptors, which are typically used for various system operations and can contain sensitive information or access rights that should not be exposed to unauthorized processes.
The operational impact of this vulnerability is substantial for local users who can exploit the flaw through custom mail-delivery programs. By crafting specific mail delivery mechanisms, an attacker can gain access to unintended file descriptors that would normally be closed during process execution. This access can potentially reveal sensitive information stored in these file descriptors, including but not limited to authentication credentials, system configuration details, or other confidential data. The vulnerability essentially creates a persistent information leakage channel that can be exploited to escalate privileges or gather intelligence about the system's internal state, making it particularly dangerous in multi-user environments or systems with sensitive data handling requirements.
The flaw aligns with CWE-665, which addresses improper initialization of resources, and can be categorized under ATT&CK technique T1059 for command and script injection, as attackers can leverage this vulnerability to execute malicious code through improperly managed file descriptors. Organizations running affected sendmail versions should prioritize immediate patching to remediate this issue, as the vulnerability provides a direct pathway for local privilege escalation and information disclosure. The recommended mitigation involves upgrading to sendmail version 8.14.9 or later, which contains the corrected argument ordering in the sm_close_on_exec function. Additionally, system administrators should review and audit mail delivery configurations to ensure that no custom delivery programs are inadvertently exploiting this vulnerability, while implementing proper monitoring for unusual file descriptor access patterns that might indicate exploitation attempts.