CVE-2011-1093 in Linux
Summary
by MITRE
The dccp_rcv_state_process function in net/dccp/input.c in the Datagram Congestion Control Protocol (DCCP) implementation in the Linux kernel before 2.6.38 does not properly handle packets for a CLOSED endpoint, which allows remote attackers to cause a denial of service (NULL pointer dereference and OOPS) by sending a DCCP-Close packet followed by a DCCP-Reset packet.
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Analysis
by VulDB Data Team • 11/14/2021
The vulnerability identified as CVE-2011-1093 resides within the Linux kernel's implementation of the Datagram Congestion Control Protocol DCCP which is designed for applications requiring reliable transport with congestion control but without the overhead of connection establishment. This flaw manifests in the dccp_rcv_state_process function located in net/dccp/input.c, where the kernel fails to properly validate incoming packets when the DCCP endpoint is in a CLOSED state. The improper handling occurs specifically when processing DCCP-Close packets followed by DCCP-Reset packets, creating a scenario where the kernel's state machine does not account for the sequence of operations that could lead to a critical system failure.
The technical exploitation of this vulnerability involves sending a carefully crafted sequence of DCCP packets to a target system running an affected Linux kernel version prior to 2.6.38. When the kernel receives the DCCP-Close packet followed by the DCCP-Reset packet, the dccp_rcv_state_process function attempts to dereference a NULL pointer in the context of a CLOSED endpoint state, resulting in a kernel NULL pointer dereference that triggers an OOPS condition. This type of error represents a fundamental flaw in kernel memory management and state validation, where the system cannot properly handle packet processing when the endpoint transitions through its lifecycle states. The vulnerability directly maps to CWE-476 which describes NULL pointer dereference issues in software implementations.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromising system stability and availability. A remote attacker can reliably trigger a system crash or reboot through this method, effectively rendering the affected system unavailable to legitimate users and applications. The vulnerability affects all systems running Linux kernel versions earlier than 2.6.38, making it particularly concerning for network infrastructure components, servers, and devices that rely on DCCP for their communication protocols. From an attacker perspective, this represents a low-effort, high-impact vector that requires minimal resources to execute against vulnerable systems.
The mitigation strategy for CVE-2011-1093 involves immediate patching of affected systems with kernel versions 2.6.38 or later, where the kernel developers have implemented proper state validation and packet handling for CLOSED endpoint scenarios. Organizations should also consider implementing network-level protections such as firewall rules that can filter or drop suspicious DCCP traffic patterns, though this approach provides only partial protection as the vulnerability exists within the kernel itself. The fix addresses the core issue by ensuring that the dccp_rcv_state_process function properly validates endpoint states before attempting to process incoming packets, preventing the NULL pointer dereference that leads to system instability. This vulnerability demonstrates the critical importance of proper state machine implementation in kernel networking code and aligns with ATT&CK technique T1499.004 for network denial of service attacks, highlighting the need for robust input validation and state management in system-level protocols.