CVE-2004-0257 in NetBSD
Summary
by MITRE
OpenBSD 3.4 and NetBSD 1.6 and 1.6.1 allow remote attackers to cause a denial of service (crash) by sending an IPv6 packet with a small MTU to a listening port and then issuing a TCP connect to that port.
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Analysis
by VulDB Data Team • 07/08/2017
This vulnerability exists in OpenBSD 3.4 and NetBSD 1.6 and 1.6.1 operating systems where a remote attacker can trigger a denial of service condition by crafting and sending specific IPv6 packets. The flaw occurs when an attacker sends an IPv6 packet with a small maximum transmission unit value to a listening port on the target system, followed by a TCP connect request to the same port. This sequence causes the system to crash and become unavailable to legitimate users. The vulnerability stems from improper handling of IPv6 packet processing in the network stack when dealing with small MTU values, particularly when combined with TCP connection attempts. The issue represents a classic buffer overflow or memory corruption scenario where the system fails to properly validate or handle the malformed packet parameters.
The technical implementation of this vulnerability involves the interaction between IPv6 packet processing and TCP connection establishment within the kernel network stack. When the system receives an IPv6 packet with a small MTU value, the kernel's IPv6 processing code does not adequately validate the packet parameters before proceeding with TCP connection handling. This leads to memory corruption or invalid pointer dereferences that ultimately result in system crash. The vulnerability is categorized under CWE-125 as an out-of-bounds read or write condition, and it aligns with ATT&CK technique T1499.004 for network denial of service attacks. The specific nature of the flaw involves improper bounds checking during IPv6 packet header processing, where the system fails to validate that the MTU value falls within acceptable ranges before attempting to establish TCP connections.
From an operational impact perspective, this vulnerability allows remote attackers to perform effective denial of service attacks against systems running the affected versions of OpenBSD or NetBSD. The attack requires minimal privileges and can be executed from any network location, making it particularly dangerous for network services that are publicly accessible. The crash resulting from this vulnerability renders the targeted system completely unavailable until manual intervention or system reboot occurs. This type of vulnerability is particularly concerning for critical infrastructure systems, web servers, and network services that cannot afford extended downtime. The attack vector demonstrates the importance of robust input validation and proper error handling in kernel-level network processing code.
Mitigation strategies for this vulnerability include applying the relevant security patches provided by OpenBSD and NetBSD development teams, which typically involve implementing proper validation of MTU values in IPv6 packet processing routines. System administrators should also consider implementing network-level filtering to restrict incoming IPv6 packets with suspicious MTU values or to drop malformed packets before they reach the kernel network stack. Additional defensive measures include monitoring network traffic for unusual patterns of IPv6 packets with small MTU values and implementing intrusion detection systems that can identify and alert on potential exploitation attempts. The vulnerability highlights the necessity of comprehensive security testing for kernel network components and demonstrates the importance of maintaining up-to-date system configurations to prevent exploitation of known vulnerabilities. Organizations should also conduct regular security audits of their network infrastructure to identify and remediate similar issues that may exist in other system components.