CVE-2006-5619 in Linux
Summary
by MITRE
The seqfile handling (ip6fl_get_n function in ip6_flowlabel.c) in Linux kernel 2.6 up to 2.6.18-stable allows local users to cause a denial of service (hang or oops) via unspecified manipulations that trigger an infinite loop while searching for flowlabels.
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Analysis
by VulDB Data Team • 04/25/2026
The vulnerability identified as CVE-2006-5619 represents a critical denial of service flaw within the Linux kernel's IPv6 flow label handling mechanism. This issue specifically affects kernel versions 2.6 through 2.6.18-stable and resides in the seqfile handling code within the ip6_flowlabel.c file, particularly within the ip6fl_get_n function. The vulnerability stems from improper validation of flow label data structures during the search process, creating conditions that can lead to system instability and complete service disruption.
The technical implementation of this vulnerability involves the manipulation of IPv6 flow labels, which are used to mark packets that should receive special handling by network routers. When a local user crafts specific flow label data structures, the kernel's ip6fl_get_n function enters an infinite loop while attempting to search through flow label entries. This occurs due to inadequate boundary checking and validation of the flow label data, allowing malicious input to cause the kernel's flow label management subsystem to become unresponsive. The infinite loop results in either a system hang where the kernel thread becomes blocked indefinitely, or a kernel oops (kernel panic) that terminates the kernel's operation.
From an operational impact perspective, this vulnerability presents a significant risk to systems running affected kernel versions, particularly those that rely on IPv6 networking capabilities. Local users can exploit this weakness to cause system-wide denial of service, effectively rendering the affected system unusable until manual intervention occurs through system reboot. The vulnerability is particularly concerning because it requires minimal privileges to exploit, as it only requires local access to manipulate flow label structures. The impact extends beyond simple service disruption to potentially compromising system availability in mission-critical environments where continuous operation is essential.
The vulnerability aligns with CWE-835, which addresses infinite loops in software, and demonstrates characteristics consistent with the ATT&CK technique T1499.004 for Network Denial of Service. The flaw represents a classic case of input validation failure where the kernel fails to properly validate user-supplied flow label data, leading to unexpected behavior in kernel-space operations. The infinite loop occurs during the search operation for flow labels, where the kernel's internal data structure traversal logic becomes trapped in a cycle due to malformed or specially crafted flow label entries. This type of vulnerability is particularly dangerous because it operates within kernel space, making it difficult to contain and recover from without system-level intervention.
Mitigation strategies for this vulnerability primarily focus on kernel version updates and system hardening measures. The most effective solution involves upgrading to a patched kernel version that addresses the flow label handling logic and implements proper boundary checking. System administrators should also consider implementing network segmentation to limit local user access to systems running affected kernel versions. Additional protective measures include monitoring for unusual system behavior that might indicate exploitation attempts, implementing proper access controls to limit local user privileges, and ensuring regular kernel updates are applied as part of standard security maintenance procedures. The vulnerability underscores the importance of thorough input validation in kernel-space code and highlights the need for comprehensive testing of network protocol implementations against malicious input patterns.