CVE-2016-6252 in shadow
Summary
by MITRE
Integer overflow in shadow 4.2.1 allows local users to gain privileges via crafted input to newuidmap.
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Analysis
by VulDB Data Team • 08/15/2020
The vulnerability identified as CVE-2016-6252 represents a critical integer overflow flaw within the shadow package version 4.2.1, specifically affecting the newuidmap utility. This issue resides in the user mapping functionality that manages the translation between user IDs and group IDs in Unix-like operating systems. The shadow package serves as a fundamental component for user account management, handling password encryption, user identification, and group membership operations across Linux distributions. When the newuidmap utility processes user input, it fails to properly validate or sanitize the input parameters, creating a scenario where an integer overflow can occur during arithmetic operations involving user ID mappings. This vulnerability specifically manifests when local users provide crafted input to the newuidmap program, which is designed to establish user mappings for the setuid environment.
The technical exploitation of this integer overflow vulnerability occurs through a carefully constructed input sequence that causes the arithmetic operations within newuidmap to exceed the maximum representable value for a signed integer. When the overflow occurs, the program's behavior becomes unpredictable and can result in the manipulation of memory addresses or control flow within the application. The overflow typically happens during calculations involving user ID ranges, where the arithmetic operation produces a value that cannot be represented within the allocated integer data type, causing the value to wrap around to a negative or unexpected positive value. This wraparound behavior can lead to improper memory allocation, buffer overflows, or other memory corruption issues that directly compromise the security boundaries of the system.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and unauthorized access to sensitive resources. Local users who can execute the newuidmap utility gain the ability to manipulate user ID mappings in ways that bypass normal access controls, potentially allowing them to elevate their privileges to root or other high-privilege accounts. The vulnerability is particularly dangerous because it leverages legitimate system utilities that are often executed with elevated privileges, making the attack vector more accessible and the exploitation more effective. In environments where multiple users share a system or where the shadow package is used in conjunction with other privilege escalation mechanisms, this vulnerability can serve as a critical stepping stone for attackers seeking persistent access to the system. The integer overflow can also potentially cause application crashes or denial of service conditions, further impacting system availability and stability.
Mitigation strategies for CVE-2016-6252 should focus on immediate patch application and system hardening measures to prevent exploitation. The primary remediation involves updating the shadow package to version 4.3 or later, which includes proper input validation and overflow protection mechanisms. System administrators should implement strict access controls on the newuidmap utility, limiting execution permissions to only trusted users and groups. The vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions, and can be categorized under ATT&CK technique T1068 for privilege escalation through local exploitation. Additional defensive measures include monitoring for suspicious execution patterns of newuidmap, implementing proper input sanitization for user-provided data, and conducting regular security audits of system utilities that handle user ID mappings. Organizations should also consider implementing privilege separation techniques and ensuring that all system components undergo regular security assessments to identify similar vulnerabilities in other software packages. The remediation process should include comprehensive testing to ensure that the patch does not introduce compatibility issues with existing user mapping configurations while maintaining the integrity of the system's user account management infrastructure.