CVE-2010-2431 in cups
Summary
by MITRE
The cupsFileOpen function in CUPS before 1.4.4 allows local users, with lp group membership, to overwrite arbitrary files via a symlink attack on the (1) /var/cache/cups/remote.cache or (2) /var/cache/cups/job.cache file.
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Analysis
by VulDB Data Team • 09/18/2021
The vulnerability described in CVE-2010-2431 represents a critical privilege escalation flaw within the Common Unix Printing System CUPS software version 1.4.3 and earlier. This issue arises from insecure file handling practices within the cupsFileOpen function, which operates with elevated privileges due to the lp group membership requirements for printing operations. The vulnerability specifically targets two cache files in the /var/cache/cups/ directory structure, making it particularly dangerous for systems where local users have access to the lp group but lack administrative privileges. The flaw enables malicious users to exploit symbolic link attacks against these cache files, potentially allowing them to overwrite arbitrary system files with the privileges of the CUPS daemon process.
The technical implementation of this vulnerability stems from the improper handling of file operations in the cupsFileOpen function, which does not adequately validate the existence and ownership of target files before opening them. When CUPS processes print jobs, it creates cache files at /var/cache/cups/remote.cache and /var/cache/cups/job.cache to maintain job state information. The vulnerability manifests when local users with lp group membership can create symbolic links that point to system files of their choice, and then trigger CUPS operations that cause the cupsFileOpen function to open these maliciously crafted symbolic links. This creates a race condition where the attacker can manipulate the file system to redirect file operations to arbitrary locations, bypassing normal access controls and privilege boundaries.
From an operational impact perspective, this vulnerability represents a significant threat to system security as it allows local users to potentially escalate their privileges and overwrite critical system files. The attack vector is particularly concerning because it requires only membership in the lp group, which is typically granted to users who need to submit print jobs. This means that any user with basic printing privileges could exploit this vulnerability to overwrite system files, potentially leading to privilege escalation, denial of service, or even complete system compromise. The vulnerability aligns with CWE-367, which describes Time-of-Check to Time-of-Use (TOCTOU) race conditions, and demonstrates how insecure file handling can create persistent security weaknesses.
The mitigation strategy for this vulnerability involves upgrading to CUPS version 1.4.4 or later, where the file handling in cupsFileOpen has been corrected to properly validate file paths and prevent symbolic link attacks. System administrators should also implement proper file system permissions and consider using file integrity monitoring tools to detect unauthorized modifications to critical cache files. Organizations should conduct regular security assessments to identify and remediate similar vulnerabilities in other system components, as this type of flaw often indicates broader issues with file access control and privilege management. The vulnerability also highlights the importance of following secure coding practices and adhering to the principle of least privilege, as demonstrated by the ATT&CK framework's emphasis on privilege escalation techniques that exploit insecure file operations.