CVE-2005-0960 in OpenBSD
Summary
by MITRE
Multiple vulnerabilities in the SACK functionality in (1) tcp_input.c and (2) tcp_usrreq.c OpenBSD 3.5 and 3.6 allow remote attackers to cause a denial of service (memory exhaustion or system crash).
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/07/2018
The vulnerability described in CVE-2005-0960 represents a critical flaw in the Transmission Control Protocol implementation within OpenBSD versions 3.5 and 3.6. This issue specifically targets the Selective Acknowledgment (SACK) functionality, which is a TCP extension designed to improve data transmission efficiency by allowing receivers to acknowledge non-contiguous data segments. The flaw manifests in two distinct code locations within the OpenBSD kernel: tcp_input.c and tcp_usrreq.c, indicating a systemic problem rather than a isolated function. These files form essential components of the TCP stack responsible for processing incoming packets and managing user-level socket requests respectively.
The technical nature of this vulnerability stems from inadequate input validation and memory management within the SACK processing code. When remote attackers send specially crafted TCP packets containing malformed SACK options, the kernel's tcp_input.c and tcp_usrreq.c functions fail to properly handle these inputs, leading to memory corruption or exhaustion conditions. The vulnerability operates at the network protocol level, exploiting weaknesses in how the kernel processes TCP acknowledgment information. This type of flaw falls under CWE-129, which addresses improper validation of length fields, and CWE-787, concerning out-of-bounds writes. The attack vector requires only network access to send malicious TCP packets, making it particularly dangerous as it can be exploited remotely without authentication.
The operational impact of this vulnerability is severe and potentially catastrophic for systems running affected OpenBSD versions. Successful exploitation can result in complete system crashes, forcing network services to become unavailable and potentially requiring system reboots. The memory exhaustion aspect can cause the system to become unresponsive as kernel memory becomes corrupted or depleted, while the system crash component can lead to data loss and service interruptions. Network administrators face the challenge of maintaining availability while patching systems, as the vulnerability affects core networking functionality. The impact extends beyond simple denial of service to potentially compromising the stability of network infrastructure, particularly in environments where OpenBSD serves as a router or firewall. This vulnerability aligns with ATT&CK technique T1499.004, which describes network disruption through resource exhaustion attacks, and represents a classic example of how protocol implementation flaws can be weaponized for system compromise.
Mitigation strategies for CVE-2005-0960 require immediate system updates to patched versions of OpenBSD, specifically versions 3.7 and later where the SACK processing vulnerabilities have been addressed. Organizations should implement network segmentation and firewall rules to limit exposure to potentially malicious traffic, though this provides only partial protection as the vulnerability affects kernel-level processing. System administrators should monitor for unusual network traffic patterns that might indicate exploitation attempts and ensure proper patch management procedures are in place. The fix typically involves proper bounds checking and memory allocation handling within the tcp_input.c and tcp_usrreq.c files, ensuring that SACK options are validated before processing. Additionally, implementing intrusion detection systems that can identify malformed TCP packets with SACK options may provide early warning of potential exploitation attempts, though this approach has limitations as the attack can be subtle and may not be easily distinguishable from legitimate traffic patterns.