CVE-2006-0381 in FreeBSD
Summary
by MITRE
A logic error in the IP fragment cache functionality in pf in FreeBSD 5.3, 5.4, and 6.0, and OpenBSD, when a scrub fragment crop or scrub fragment drop-ovl rule is being used, allows remote attackers to cause a denial of service (crash) via crafted packets that cause a packet fragment to be inserted twice.
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Analysis
by VulDB Data Team • 03/12/2021
The vulnerability identified as CVE-2006-0381 represents a critical logic error within the packet filtering subsystem of FreeBSD and OpenBSD operating systems. This flaw specifically targets the IP fragment cache functionality within the pf packet filter implementation, which serves as a fundamental security mechanism for network traffic control and filtering. The vulnerability manifests when the system processes packets that trigger either a scrub fragment crop or scrub fragment drop-ovl rule, creating a scenario where malformed packet fragments can be processed in a manner that leads to system instability.
The technical implementation of this vulnerability stems from a flaw in how the packet filtering system handles duplicate fragment insertion within its caching mechanism. When crafted packets are transmitted to a vulnerable system, they exploit a race condition or logic flaw in the fragment cache management, causing the system to attempt to insert the same packet fragment twice into the cache structure. This double insertion results in memory corruption within the kernel's packet processing subsystem, ultimately leading to a system crash and subsequent denial of service condition. The vulnerability operates at the network layer and specifically affects the kernel's handling of IP fragmentation reassembly.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire network security posture of affected systems. Remote attackers can leverage this flaw to perform denial of service attacks against network infrastructure without requiring authentication or elevated privileges. The vulnerability affects multiple versions of FreeBSD including 5.3, 5.4, and 6.0, along with OpenBSD systems, making it a widespread concern for network administrators maintaining legacy systems. When exploited, the vulnerability can cause complete system crashes, requiring manual intervention and system restarts that may result in extended downtime and potential data loss.
Mitigation strategies for this vulnerability require immediate system updates and patches from the respective operating system vendors. System administrators should prioritize upgrading to patched versions of FreeBSD and OpenBSD that address the fragment cache logic error. Additionally, network administrators can implement temporary workarounds such as disabling specific fragment processing rules or implementing additional network filtering to prevent malformed packets from reaching vulnerable systems. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and maps to ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also consider implementing intrusion detection systems to monitor for exploitation attempts and establish incident response procedures to handle potential system crashes and recovery operations.