CVE-2004-1031 in fcron
Summary
by MITRE
fcronsighup in fcron 2.0.1 2.9.4 and possibly earlier versions allows local users to bypass access restrictions and load an arbitrary configuration file by starting an suid process and pointing the fcronsighup configuration file to a /proc entry that is owned by root but modifiable by the user such as /proc/self/cmdline or /proc/self/environ.
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Analysis
by VulDB Data Team • 06/02/2019
The vulnerability described in CVE-2004-1031 represents a critical privilege escalation flaw within the fcron daemon software version 2.0.1 through 2.9.4 and potentially earlier releases. This issue arises from improper access control mechanisms within the fcronsighup utility, which is designed to handle signal processing for the fcron scheduling system. The flaw enables local attackers to circumvent security restrictions that should normally prevent unauthorized access to sensitive system configuration files.
The technical implementation of this vulnerability exploits the specific behavior of the /proc filesystem in Linux operating systems where certain process-related entries such as /proc/self/cmdline and /proc/self/environ are owned by root but can be modified by regular users. When fcronsighup processes configuration files, it fails to properly validate the ownership and permissions of the target files, allowing malicious users to create symbolic links or manipulate these specific /proc entries to point to arbitrary configuration files. This misconfiguration creates a path where a local user can effectively load a malicious configuration file with elevated privileges, bypassing the intended security boundaries.
The operational impact of this vulnerability is significant as it allows local users to escalate their privileges to root level access, potentially compromising the entire system. Attackers can leverage this flaw to execute arbitrary code with the highest system privileges, modify critical system files, install backdoors, or perform other malicious activities that would normally be restricted. The vulnerability is particularly dangerous because it requires minimal privileges to exploit and can be combined with other techniques to establish persistent access to the compromised system.
The root cause of this vulnerability aligns with CWE-276, which describes improper file permissions and access control issues. The flaw demonstrates a classic case of insufficient privilege checking where the application fails to properly validate file ownership and access permissions before processing configuration files. This vulnerability also maps to ATT&CK technique T1068, which covers "Local Privilege Escalation" through the exploitation of system configuration weaknesses. Organizations should immediately implement mitigations including updating to patched versions of fcron, reviewing and hardening /proc filesystem permissions, and implementing proper access controls for critical system utilities. Additionally, system administrators should consider implementing mandatory access controls and monitoring for unauthorized changes to critical system files.
The vulnerability highlights the importance of proper privilege separation and access control validation in system-level utilities. When applications handle configuration files with elevated privileges, they must implement rigorous checks to ensure that only authorized users can modify or access sensitive resources. This particular flaw demonstrates how seemingly innocuous file system behavior can create significant security risks when not properly accounted for in security design. The exploitation of such vulnerabilities often requires a deep understanding of the underlying operating system mechanisms and can be particularly challenging to detect through standard security monitoring approaches.