Buffer overflow in Linux Slackware crond program allows local users to gain root access.
Critical vulnerability discovered in the Slackware crond program allows attackers to achieve root-level access on vulnerable Linux systems via a buffer overflow. Successful exploitation grants complete control over the compromised server, enabling data theft, system compromise, and lateral movement within the network.
Step 1: Triggering the Vulnerability: The attacker crafts a malicious input, likely a specially crafted crontab entry or environment variable, designed to overflow a buffer within the crond program. This input is submitted to the crond service, either directly or indirectly through a user account with crontab privileges.
Step 2: Buffer Overflow: The crond program processes the malicious input. Due to the lack of bounds checking, the input overflows a designated buffer within the program's memory space.
Step 3: Overwriting Memory: The overflow overwrites adjacent memory locations, including the return address on the stack. This return address points to the location in memory where the program should resume execution after the current function completes.
Step 4: Shellcode Injection: The attacker's crafted input includes shellcode (malicious code) designed to execute with root privileges. This shellcode is placed within the overflowed buffer.
Step 5: Code Execution: When the vulnerable function completes, the program attempts to return to the overwritten return address. Instead of returning to the original location, it jumps to the attacker's shellcode within the buffer, granting the attacker root privileges.
The vulnerability stems from a buffer overflow in the crond program, likely related to how it handles input or processes commands. The root cause is the lack of proper bounds checking when processing input, leading to the overflow. Specifically, the program doesn't validate the size of the data it receives, allowing an attacker to write data beyond the allocated buffer, overwriting adjacent memory regions, including critical program data or control flow structures. This allows an attacker to overwrite the return address on the stack, redirecting program execution to malicious code (shellcode) injected into the overflowed buffer. The specific function or logic flaw is likely related to how crond parses or processes job definitions or command arguments, potentially within the context of how it handles environment variables or command line parameters. The lack of input validation is the primary root cause.