CVE-2016-7091 in sudo
Summary
by MITRE
sudo: It was discovered that the default sudo configuration on Red Hat Enterprise Linux and possibly other Linux implementations preserves the value of INPUTRC which could lead to information disclosure. A local user with sudo access to a restricted program that uses readline could use this flaw to read content from specially formatted files with elevated privileges provided by sudo.
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Analysis
by VulDB Data Team • 09/23/2024
The vulnerability identified as CVE-2016-7091 represents a critical information disclosure flaw in the sudo command implementation across Red Hat Enterprise Linux and similar Linux distributions. This issue stems from the improper handling of environment variables during privilege escalation processes, specifically concerning the INPUTRC variable that controls readline library behavior. The flaw allows local users with sudo access to potentially read content from specially crafted files that would otherwise be restricted, creating a significant security risk in environments where sudo is widely used for privilege management.
The technical root cause of this vulnerability lies in how sudo processes environment variables when executing commands with elevated privileges. The INPUTRC environment variable, which typically points to readline configuration files, is preserved during the sudo execution context. When a user with sudo privileges executes a program that utilizes the readline library, the INPUTRC variable retains its original value, potentially allowing access to files that contain sensitive information. This behavior creates a pathway for privilege escalation through information disclosure, as the readline library may attempt to read configuration files that contain credentials, system information, or other sensitive data.
From an operational impact perspective, this vulnerability affects systems where sudo is configured to allow users to execute specific programs with elevated privileges. The risk is particularly pronounced in environments where users have access to programs that utilize readline functionality, such as interactive shells, database clients, or system administration tools. Attackers could exploit this flaw by crafting specially formatted files that contain sensitive information and placing them in locations accessible through the INPUTRC variable path, thereby gaining elevated access to data that should remain protected.
The vulnerability aligns with CWE-200, which describes improper handling of environment variables leading to information disclosure, and relates to ATT&CK technique T1068, which covers privilege escalation through environment variable manipulation. Organizations using sudo for privilege management are particularly vulnerable, as the flaw does not require external network access or complex attack vectors. The impact extends beyond simple information disclosure, as the ability to read sensitive files through elevated privileges could lead to further exploitation, including credential theft, system reconnaissance, and potential lateral movement within compromised environments.
Mitigation strategies for this vulnerability include updating sudo to versions that properly sanitize environment variables during privilege escalation, implementing strict input validation for programs that utilize readline, and configuring sudo to explicitly unset or override the INPUTRC variable. System administrators should also review sudo configurations to ensure that unnecessary environment variables are not preserved during privilege escalation, and consider implementing additional monitoring for unusual file access patterns that might indicate exploitation attempts. The most effective long-term solution involves patching affected systems with updated sudo versions that address this specific environment variable handling flaw, while maintaining regular security assessments to identify similar vulnerabilities in other system components.