CVE-2005-0740 in OpenBSD
Summary
by MITRE
The TCP stack (tcp_input.c) in OpenBSD 3.5 and 3.6 allows remote attackers to cause a denial of service (system panic) via crafted values in the TCP timestamp option, which causes invalid arguments to be used when calculating the retransmit timeout.
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Analysis
by VulDB Data Team • 06/30/2019
The vulnerability described in CVE-2005-0740 represents a critical flaw in the OpenBSD operating system's TCP implementation that specifically affects versions 3.5 and 3.6. This issue resides within the tcp_input.c file, which is responsible for processing incoming TCP packets and managing the transmission control protocol's core functionalities. The vulnerability stems from inadequate validation of TCP timestamp options, which are used to calculate retransmission timeouts and ensure proper network communication. When remote attackers craft malicious TCP packets containing malformed timestamp values, the system's TCP stack fails to properly handle these invalid inputs, leading to a system panic that effectively causes a denial of service condition.
The technical root cause of this vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and specifically relates to the improper handling of TCP timestamp options within the retransmission timeout calculation mechanism. The flaw occurs when the TCP stack processes TCP packets containing crafted timestamp values that fall outside the expected parameter ranges or violate mathematical constraints required for timeout calculations. These invalid timestamp values, when processed through the retransmission timeout calculation algorithms, result in arithmetic operations that produce invalid parameters for internal system functions, ultimately triggering a kernel panic that crashes the entire system.
From an operational perspective, this vulnerability presents a severe threat to network infrastructure relying on OpenBSD systems, as it allows remote attackers to execute denial of service attacks without requiring any authentication or privileged access. The impact extends beyond simple service disruption since a system panic can result in complete system shutdown, requiring manual intervention and potentially causing significant downtime for services hosted on affected systems. Network administrators face the challenge of defending against attacks that can be executed from anywhere on the internet, making this vulnerability particularly dangerous for publicly accessible servers and network equipment running these specific OpenBSD versions.
The attack vector for this vulnerability is straightforward and highly effective, as it requires only the ability to send crafted TCP packets to the target system. Attackers can construct TCP packets with malformed timestamp options that exploit the mathematical edge cases in the retransmission timeout calculation, causing the kernel to crash when processing these invalid inputs. This vulnerability demonstrates the importance of robust input validation in kernel-level network code and highlights the potential for seemingly minor protocol implementation flaws to result in complete system compromise. Organizations should implement immediate mitigation strategies including system updates to patched versions, network segmentation to limit exposure, and monitoring for suspicious TCP traffic patterns that may indicate exploitation attempts.
This vulnerability also connects to broader security principles outlined in the ATT&CK framework under the T1499 category for network denial of service, where adversaries leverage protocol implementation flaws to disrupt system availability. The incident underscores the critical need for comprehensive security testing of network protocol implementations, particularly in kernel space where errors can result in system-wide failures. The remediation approach should include not only applying the relevant security patches but also implementing network monitoring solutions that can detect and alert on malformed TCP timestamp options, providing early warning capabilities for potential exploitation attempts.