CVE-2013-2851 in Linux
Summary
by MITRE
Format string vulnerability in the register_disk function in block/genhd.c in the Linux kernel through 3.9.4 allows local users to gain privileges by leveraging root access and writing format string specifiers to /sys/module/md_mod/parameters/new_array in order to create a crafted /dev/md device name.
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Analysis
by VulDB Data Team • 05/14/2021
The vulnerability described in CVE-2013-2851 represents a critical format string flaw within the Linux kernel's device management subsystem, specifically affecting versions through 3.9.4. This issue resides in the register_disk function located in block/genhd.c, which handles the registration of block devices within the kernel's storage framework. The vulnerability is particularly concerning because it allows local attackers with root access to escalate their privileges through a sophisticated exploitation technique that leverages the kernel's handling of device names and parameters.
The technical flaw manifests when the kernel processes format string specifiers in the md_mod module parameters, specifically in the /sys/module/md_mod/parameters/new_array interface. When a crafted device name is written to this parameter, the kernel's register_disk function fails to properly sanitize the input before using it in a format string operation. This creates an opportunity for attackers to inject format specifiers that can be exploited to read from arbitrary memory locations or even write to specific memory addresses, depending on the kernel's implementation details. The vulnerability is classified under CWE-134 which specifically addresses the use of format strings with user-supplied data without proper validation or sanitization.
The operational impact of this vulnerability is significant as it enables privilege escalation from root level access to potentially full system compromise. An attacker who already possesses root privileges can leverage this flaw to execute arbitrary code with the highest possible privileges, effectively bypassing kernel security mechanisms. The exploitation requires the attacker to have root access initially, but the vulnerability creates a path for further escalation or allows for more sophisticated attacks that could be used to manipulate kernel memory, read sensitive information, or even modify kernel data structures. This type of vulnerability is particularly dangerous in environments where root access might be obtained through other means, as it provides a reliable path to complete system compromise.
The attack vector for this vulnerability involves writing crafted format string specifiers to the /sys/module/md_mod/parameters/new_array parameter, which then gets processed by the vulnerable register_disk function. This approach demonstrates the kernel's inadequate input validation when handling device names and module parameters, particularly in the context of md (multiple device) RAID subsystem management. The vulnerability highlights the importance of proper input sanitization in kernel space code and the dangers of allowing user-supplied data to directly influence format string operations. From an ATT&CK perspective, this vulnerability aligns with privilege escalation techniques and can be categorized under techniques that involve kernel exploitation and memory manipulation. Mitigation strategies should focus on kernel updates to versions that address this specific format string vulnerability, along with implementing proper input validation and sanitization in kernel modules that handle device names and parameters. System administrators should also consider restricting access to sensitive kernel parameters and monitoring for suspicious writes to /sys/module/ directories, as these are often indicators of attempted exploitation.