CVE-2015-8767 in Linux
Summary
by MITRE
net/sctp/sm_sideeffect.c in the Linux kernel before 4.3 does not properly manage the relationship between a lock and a socket, which allows local users to cause a denial of service (deadlock) via a crafted sctp_accept call.
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Analysis
by VulDB Data Team • 07/07/2022
The vulnerability described in CVE-2015-8767 resides within the Linux kernel's Stream Control Transmission Protocol implementation, specifically in the file net/sctp/sm_sideeffect.c. This issue represents a critical race condition and locking mechanism failure that affects systems running Linux kernel versions prior to 4.3. The flaw manifests when the kernel fails to properly manage the relationship between a lock and a socket during SCTP connection handling, creating a scenario where concurrent operations can lead to system-wide deadlock conditions. The vulnerability is particularly concerning because it operates at the kernel level, meaning that a local user with minimal privileges can exploit this weakness to cause system-wide denial of service.
The technical root cause of this vulnerability stems from improper synchronization mechanisms within the SCTP state machine implementation. When a crafted sctp_accept call is made, the kernel's locking strategy becomes compromised, leading to situations where multiple threads or processes become indefinitely blocked waiting for resources that will never become available. This occurs because the lock management does not adequately account for the socket state transitions that occur during the SCTP accept operation. The flaw specifically involves the interaction between the socket lock and the state machine side effects, creating a circular dependency that results in deadlock conditions. This type of vulnerability falls under CWE-362, which describes a race condition in the context of concurrent execution and improper locking mechanisms.
The operational impact of CVE-2015-8767 extends beyond simple system unavailability as it can affect entire network services that rely on SCTP connectivity. Local users can exploit this vulnerability to cause denial of service across multiple network applications, potentially disrupting critical infrastructure services that depend on reliable socket operations. The attack vector requires only local system access, making it particularly dangerous as it can be exploited by malicious users with limited privileges or compromised accounts. This vulnerability directly aligns with ATT&CK technique T1499.004, which involves network disruption through denial of service attacks, and represents a significant weakening of system integrity and availability. The impact is amplified in environments where SCTP is heavily utilized for signaling protocols, telecommunications services, or other mission-critical applications.
Mitigation strategies for this vulnerability primarily involve upgrading to Linux kernel version 4.3 or later, where the locking mechanisms have been properly addressed. System administrators should prioritize patching affected systems, particularly those running older kernel versions that may be exposed to local privilege escalation scenarios. Additionally, monitoring for unusual socket behavior or system lockups that could indicate exploitation attempts should be implemented. Network segmentation and access controls can help limit the potential impact of local exploitation, while comprehensive system hardening practices should be applied to reduce overall attack surface. The fix implemented in kernel 4.3 addresses the core synchronization issues by properly managing the relationship between socket locks and state machine transitions, ensuring that resource acquisition and release follows correct ordering principles to prevent deadlock conditions.