CVE-2016-6318 in CrackLib
Summary
by MITRE
Stack-based buffer overflow in the FascistGecosUser function in lib/fascist.c in cracklib allows local users to cause a denial of service (application crash) or gain privileges via a long GECOS field, involving longbuffer.
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Analysis
by VulDB Data Team • 09/25/2024
The vulnerability identified as CVE-2016-6318 represents a critical stack-based buffer overflow flaw within the cracklib library's FascistGecosUser function. This vulnerability resides in the lib/fascist.c source file and demonstrates a classic security weakness where insufficient input validation leads to memory corruption. The flaw specifically manifests when processing user GECOS fields, which are traditionally used to store user information in Unix-like operating systems including full names, phone numbers, and other descriptive details. The vulnerability's classification as a stack-based buffer overflow indicates that the malicious input overflows the allocated stack memory space, potentially corrupting adjacent memory locations and leading to unpredictable application behavior.
The technical exploitation of this vulnerability occurs through the manipulation of GECOS field values that exceed the allocated buffer size within the FascistGecosUser function. When a local attacker provides an excessively long GECOS field value, the function fails to properly validate the input length before copying it into a fixed-size stack buffer. This condition creates a scenario where the overflow can overwrite adjacent stack variables, return addresses, or other critical memory structures. The vulnerability's impact extends beyond simple denial of service, as the buffer overflow could potentially be leveraged for privilege escalation depending on the execution context and memory layout. According to CWE classification, this represents a CWE-121: Stack-based Buffer Overflow, which is a well-documented and dangerous class of vulnerability that has been exploited in numerous security incidents throughout the computing industry.
The operational impact of CVE-2016-6318 affects systems that utilize cracklib for password policy enforcement, particularly in Unix and Linux environments where user account management relies on GECOS field validation. Local users with the ability to modify their own account information or create new user accounts can trigger this vulnerability, potentially causing application crashes that result in denial of service for legitimate users. More concerning is the potential for privilege escalation when the vulnerable application runs with elevated privileges, as the buffer overflow could allow attackers to manipulate program execution flow. The attack vector requires local access and involves manipulating the GECOS field during user account creation or modification, making it accessible to users who have basic system access but not necessarily administrative privileges. This vulnerability directly aligns with ATT&CK technique T1068: Exploitation for Privilege Escalation, as the buffer overflow could be weaponized to gain elevated system privileges.
Mitigation strategies for CVE-2016-6318 focus on both immediate code-level fixes and broader system hardening approaches. The primary solution involves implementing proper input validation within the FascistGecosUser function to ensure that GECOS field values do not exceed the allocated buffer size, typically through bounds checking and length validation before any memory operations occur. System administrators should also apply the latest security patches from the cracklib maintainers, as this vulnerability has been addressed in updated versions of the library. Additional protective measures include implementing proper access controls to limit user ability to modify GECOS fields, monitoring for unusual account modifications, and conducting regular security assessments of system libraries. The vulnerability underscores the importance of input validation and proper memory management practices in security-critical code, as highlighted by industry standards such as the OWASP Top Ten and NIST cybersecurity guidelines. Organizations should also consider implementing runtime protections such as stack canaries and address space layout randomization to mitigate potential exploitation of similar buffer overflow vulnerabilities in their systems.