Source: cve@mitre.org
Buffer overflow in CrackLib 2.5 may allow local users to gain root privileges via a long GECOS field.
CrackLib 2.5 is vulnerable to a buffer overflow that could allow local attackers to gain root privileges. Exploiting this vulnerability involves overflowing a buffer within the GECOS field, leading to arbitrary code execution and system compromise. This is a critical vulnerability due to its potential for complete system takeover.
Step 1: Input Preparation: The attacker crafts a long string to be used as the GECOS field. This string is designed to overflow the buffer allocated for the GECOS field in the vulnerable CrackLib code.
Step 2: Payload Delivery: The attacker provides the crafted GECOS string to a process that utilizes CrackLib, such as a program that allows user profile updates or password changes. This could be done through a local login or a service that interacts with user accounts.
Step 3: Buffer Overflow: The vulnerable CrackLib code processes the GECOS field. Due to the lack of bounds checking, the long string overflows the allocated buffer, overwriting adjacent memory on the stack.
Step 4: Control Hijacking: The attacker's crafted input overwrites the return address on the stack. This return address is then set to point to the attacker's shellcode or a gadget within the program's memory space.
Step 5: Code Execution: When the function that processed the GECOS field returns, the CPU jumps to the attacker-controlled address. This executes the attacker's shellcode, granting them root privileges.
The vulnerability lies within CrackLib 2.5's handling of the GECOS field, typically used for user profile information. Specifically, the cracklib library, when processing a user's GECOS field, fails to properly validate the length of the input. This leads to a buffer overflow when a long string is provided in the GECOS field. The overflow overwrites adjacent memory, potentially including the return address of a function call. By carefully crafting the input, an attacker can overwrite the return address with the address of malicious code (e.g., a shellcode) or a gadget within the program's memory space, leading to arbitrary code execution with the privileges of the user running the vulnerable process, which in this case, could be root if the process is running with elevated privileges. The root cause is a lack of bounds checking on the input length before copying data into a fixed-size buffer. This is a classic example of a stack-based buffer overflow.
Due to the age of the vulnerability, it's unlikely to be directly targeted by sophisticated APTs. However, it could be leveraged in conjunction with other vulnerabilities as part of a multi-stage attack. It's more likely to be exploited by opportunistic attackers or as part of automated vulnerability scanning. CISA KEV status: Not Listed
Monitor system logs for unusually long GECOS field entries, especially during user account creation or modification.
Analyze core dumps or memory snapshots for evidence of stack corruption or overwritten return addresses.
Implement file integrity monitoring to detect changes to critical system files, such as /etc/passwd or /etc/shadow, which could indicate a successful exploit.
Network intrusion detection systems (IDS) might detect unusual network traffic patterns associated with exploitation attempts, particularly if the attack involves remote access.
Use static and dynamic analysis tools to identify the presence of CrackLib 2.5 and related vulnerable functions.
Monitor for suspicious processes or commands executed with elevated privileges.
Upgrade to a patched version of CrackLib or a more recent version that addresses the buffer overflow vulnerability. If upgrading is not possible, consider disabling or restricting the functionality that uses CrackLib.
Implement input validation to limit the length of the GECOS field to a reasonable size.
Apply security patches to the operating system and any software that uses CrackLib.
Use address space layout randomization (ASLR) and data execution prevention (DEP) to mitigate the impact of buffer overflows, even if they occur.
Review and restrict the permissions of any processes that utilize CrackLib to the minimum necessary.
Implement a robust intrusion detection and prevention system (IDPS) to monitor for and block malicious activity.