CVE-2013-0265 in xnbd
Summary
by MITRE
The redirect_stderr function in xnbd_common.c in xnbd-server and xndb-wrapper in xNBD 0.1.0 allow local users to overwrite arbitrary files via a symlink attack on /tmp/xnbd.log.
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Analysis
by VulDB Data Team • 02/25/2019
The vulnerability identified as CVE-2013-0265 represents a critical file system security flaw affecting the xNBD 0.1.0 software suite, specifically within the xnbd_common.c component and xndb-wrapper utilities. This issue stems from improper handling of temporary files during the redirect_stderr function execution, creating a predictable race condition that malicious local users can exploit to gain unauthorized file system access. The vulnerability manifests through a symlink attack against the hardcoded /tmp/xnbd.log temporary file location, allowing attackers to manipulate the system's standard error redirection mechanism.
The technical implementation of this vulnerability follows a classic symlink race condition pattern where the application creates a temporary file without proper atomic operations or file descriptor validation. When the redirect_stderr function executes, it opens the /tmp/xnbd.log file for writing, but does not verify whether the target path is a legitimate file or a symbolic link. This creates an exploitable window where a local attacker can establish a symbolic link pointing to any desired file system location before the vulnerable application opens the temporary file. The flaw directly maps to CWE-367, which describes the dangerous use of a predictable temporary file location, and falls under the broader category of CWE-22, representing improper limitation of a pathname to a restricted directory.
The operational impact of this vulnerability extends beyond simple file overwriting capabilities, as it provides attackers with the potential to modify critical system files, inject malicious code into running processes, or escalate privileges within the system. Local users who can execute the xNBD server processes gain the ability to overwrite files with arbitrary content, potentially compromising system integrity, confidentiality, and availability. The vulnerability affects all systems running xNBD 0.1.0 where the service executes with elevated privileges, as the symlink attack can be leveraged to target files that would otherwise be protected from regular user access. This issue aligns with ATT&CK technique T1059.001, which covers command and scripting interpreter execution, and T1078.004, representing valid accounts with default passwords, as attackers can exploit this weakness to maintain persistent access through file system modifications.
Mitigation strategies for CVE-2013-0265 require immediate implementation of several protective measures including updating to a patched version of xNBD software, implementing proper file descriptor validation before temporary file operations, and ensuring that all temporary files are created with appropriate permissions and atomic operations. System administrators should also consider implementing restrictive file system permissions for temporary directories, particularly /tmp, and employ file system monitoring to detect unauthorized symbolic link creation. Additionally, the vulnerability highlights the importance of following secure coding practices such as those outlined in the OWASP Secure Coding Practices, specifically addressing the prevention of predictable temporary file usage and implementing proper access controls for system resources. Organizations should conduct immediate vulnerability assessments to identify systems running affected versions and implement comprehensive monitoring to detect potential exploitation attempts.