CVE-2015-1421 in Linux
Summary
by MITRE
Use-after-free vulnerability in the sctp_assoc_update function in net/sctp/associola.c in the Linux kernel before 3.18.8 allows remote attackers to cause a denial of service (slab corruption and panic) or possibly have unspecified other impact by triggering an INIT collision that leads to improper handling of shared-key data.
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Analysis
by VulDB Data Team • 03/08/2022
The CVE-2015-1421 vulnerability represents a critical use-after-free flaw within the Linux kernel's Stream Control Transmission Protocol implementation, specifically affecting versions prior to 3.18.8. This vulnerability resides in the sctp_assoc_update function located in net/sctp/associola.c, where improper memory management during SCTP association updates creates a dangerous condition that can be exploited by remote attackers. The flaw manifests when an INIT collision occurs during the SCTP handshake process, which is a scenario where two endpoints simultaneously attempt to establish an association, leading to complex state management challenges within the kernel's networking stack. The vulnerability's impact extends beyond simple denial of service, as the use-after-free condition can potentially lead to more severe consequences including system crashes, slab corruption, and in some cases, unspecified other impacts that could compromise system stability.
The technical exploitation of this vulnerability relies on the attacker's ability to trigger an INIT collision scenario, which forces the kernel to handle shared-key data in an improper manner. During normal SCTP operations, when an INIT message is received, the kernel must properly manage memory allocations for association structures and shared-key information. However, the flawed sctp_assoc_update function fails to correctly release memory references before reassigning them, creating a window where freed memory can be accessed and potentially overwritten. This memory management error falls under the CWE-416 category of Use After Free, which is a well-documented vulnerability pattern where software continues to use a pointer after the memory it points to has been freed. The specific nature of the flaw involves improper handling of reference counting and memory deallocation during association state transitions, where the kernel's SCTP implementation does not adequately protect against concurrent access patterns that could lead to memory corruption.
The operational impact of this vulnerability is significant for systems running affected Linux kernel versions, as it can be triggered remotely without requiring authentication or special privileges. Attackers can leverage this vulnerability to cause system instability through denial of service attacks that result in kernel panics and system crashes. The slab corruption that occurs during exploitation can potentially lead to more serious consequences, as the kernel's memory allocator (slab allocator) becomes corrupted, which may allow for further exploitation or compromise of system resources. The vulnerability affects the core networking functionality of Linux systems, making it particularly dangerous in server environments where continuous availability is critical. Systems that rely heavily on SCTP for communication protocols such as telecommunications signaling, financial transactions, or real-time applications are especially vulnerable to this type of attack, as the exploitation can disrupt critical services and potentially lead to data loss or service interruption. The vulnerability's remote exploitability means that attackers can target systems from outside the local network, making it a serious concern for network administrators and security teams.
Mitigation strategies for CVE-2015-1421 primarily focus on kernel version updates, which is the most effective and recommended approach for addressing this vulnerability. System administrators should immediately upgrade to Linux kernel versions 3.18.8 or later, where the memory management issues in the sctp_assoc_update function have been properly resolved through corrected reference counting and memory deallocation procedures. Additionally, network administrators can implement temporary network-level mitigations such as firewall rules that restrict SCTP traffic or disable SCTP functionality if it is not essential for the system's operation. The fix implemented in the patched kernel versions addresses the root cause by ensuring proper memory management during association updates and implementing appropriate locking mechanisms to prevent race conditions that could lead to use-after-free conditions. Organizations should also consider monitoring for unusual network traffic patterns that might indicate exploitation attempts, as the vulnerability's exploitation typically involves specific SCTP message sequences that could be detected through network analysis. The ATT&CK framework categorizes this vulnerability under the T1499 category of Network Denial of Service, with potential for T1059 command and control execution if exploitation leads to further system compromise, making comprehensive monitoring and patch management essential for maintaining system security.