Source: cve@mitre.org
Buffer overflow in Vixie Cron library up to version 3.0 allows local users to obtain root access via a long environmental variable.
Vixie Cron, a widely used scheduling utility, is vulnerable to a buffer overflow that allows attackers to gain root privileges. Exploiting this vulnerability involves crafting a malicious environmental variable, leading to complete system compromise. This poses a significant risk to systems running vulnerable versions of Vixie Cron.
Step 1: Environment Variable Setup: The attacker crafts a malicious environment variable with a length exceeding the buffer size allocated within the Vixie Cron daemon.
Step 2: Cron Job Execution: The attacker either creates a cron job that utilizes the crafted environment variable or manipulates an existing cron job to trigger the vulnerability.
Step 3: Daemon Processing: When the cron daemon executes the job, it attempts to copy the attacker-controlled environment variable into its internal buffer.
Step 4: Buffer Overflow: The oversized environment variable overflows the buffer, overwriting adjacent memory locations, including the return address.
Step 5: Code Injection: The attacker's crafted environment variable includes shellcode or a pointer to shellcode, which is then executed when the cron daemon returns from the function.
Step 6: Privilege Escalation: The injected shellcode executes with root privileges, granting the attacker complete control over the system.
The vulnerability lies within the Vixie Cron library, specifically in how it handles environmental variables. When processing a cron job, the cron daemon copies environment variables into a fixed-size buffer. A long environmental variable, exceeding the buffer's capacity, overwrites adjacent memory regions, triggering a buffer overflow. This overwrite can corrupt critical data structures, including the return address, allowing an attacker to inject and execute arbitrary code with root privileges. The root cause is a lack of bounds checking when copying the environment variables, leading to the overflow.
While no specific APTs are definitively linked to this specific CVE, the ease of exploitation and potential for root access makes it a target for various threat actors. This type of vulnerability is often used by attackers to gain initial access and escalate privileges. This CVE is not listed in the CISA KEV catalog, but it is a high-severity vulnerability.
Monitor system logs (e.g., /var/log/syslog, /var/log/cron) for suspicious cron job activity, especially those involving unusual environment variables or commands.
Analyze core dumps or memory snapshots for signs of buffer overflows in the cron daemon process.
Use intrusion detection systems (IDS) and intrusion prevention systems (IPS) with signatures designed to detect buffer overflow attempts.
Monitor for changes to the cron.allow and cron.deny files, as attackers may attempt to modify these to gain access.
Upgrade Vixie Cron to a patched version (3.0.1 or later).
Implement least privilege principles, limiting the permissions of users who can create or modify cron jobs.
Regularly audit cron jobs for suspicious commands or environment variables.
Employ a host-based intrusion detection system (HIDS) to monitor for malicious activity.
Implement a web application firewall (WAF) to filter malicious requests.