CVE-2026-72392 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
ipv6: fib6: fix NULL deref in fib6_walk_continue() on multi-batch dump
inet6_dump_fib() saves its progress in cb->args[1] as a positional
index within the current hash chain. Between batches, a concurrent fib6_new_table() can insert a new table at the chain head, shifting all existing entries. The saved index then lands on a different table, causing fib6_dump_table() to set w->root to the wrong table while w->node still points into the previous one. fib6_walk_continue() dereferences w->node->parent (NULL) and panics:
BUG: kernel NULL pointer dereference, address: 0000000000000008 RIP: 0010:fib6_walk_continue+0x6e/0x170 Call Trace: <TASK> fib6_dump_table.isra.0+0xc5/0x240 inet6_dump_fib+0xf6/0x420 rtnl_dumpit+0x30/0xa0 netlink_dump+0x15b/0x460 netlink_recvmsg+0x1d6/0x2a0 ____sys_recvmsg+0x17a/0x190
Fix by storing tb->tb6_id in cb->args[1] instead of a positional
index. On resume, skip entries until the id matches; a concurrent head-insert can never match the saved id, so the walker always resumes on the correct table.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the Linux kernel's IPv6 forwarding information base implementation where a null pointer dereference occurs during fib6_walk_continue() execution when processing multi-batch dump operations. The issue stems from how inet6_dump_fib() maintains its iteration progress using cb->args[1] to store a positional index within hash chains, creating a race condition scenario between batch processing and concurrent table modifications.
The technical flaw manifests when a concurrent fib6_new_table() operation inserts a new table at the head of an existing hash chain, causing all subsequent entries to shift positions. This repositioning invalidates the previously saved index stored in cb->args[1], leading to incorrect table reference resolution where fib6_dump_table() sets w->root to one table while w->node continues pointing into another. When fib6_walk_continue() attempts to dereference w->node->parent, it encounters a null pointer at address 0000000000000008 causing kernel panic and system instability.
This vulnerability aligns with CWE-476 Null Pointer Dereference and represents a classic race condition in kernel data structure management. The operational impact includes potential system crashes, denial of service conditions, and compromised network functionality during IPv6 routing table enumeration operations. Attackers could potentially exploit this by triggering concurrent table modifications during dump operations, though the vulnerability requires specific timing conditions and concurrent access patterns typical in high-traffic network environments.
The fix implements a more robust approach by storing tb->tb6_id in cb->args[1] instead of positional indices, ensuring that when resuming iteration, the system skips entries until matching the saved table identifier. This prevents the race condition where a concurrent head-insert operation could cause incorrect table reference resolution since such operations cannot match the previously saved table id. The solution follows established kernel security patterns for maintaining state consistency during concurrent data structure access, addressing the root cause rather than merely patching symptoms.
This issue demonstrates the complexity of kernel-level synchronization problems in high-concurrency environments and highlights the importance of proper state management during multi-step operations involving shared data structures. The mitigation strategy aligns with ATT&CK technique T1499.004 for operating system binary proxies, ensuring that the fix maintains both correctness and performance characteristics while preventing the specific null pointer dereference scenario that led to system crashes.
The vulnerability affects Linux kernel versions where IPv6 forwarding information base operations are performed in multi-batch dump scenarios, particularly impacting network services requiring continuous routing table monitoring. Systems running high-traffic IPv6 networks or those performing frequent routing table enumeration operations would be most susceptible to exploitation attempts targeting this specific race condition. The fix maintains backward compatibility while providing robust protection against concurrent modification scenarios that could otherwise lead to system instability and potential denial of service conditions.
This security patch exemplifies the critical nature of kernel-level vulnerabilities in networking subsystems where improper synchronization can lead to complete system crashes. The implementation demonstrates proper defensive programming practices by ensuring state consistency during concurrent access patterns, a fundamental requirement for maintaining system integrity in multi-threaded kernel environments. The solution prevents attackers from leveraging timing-based race conditions to achieve privilege escalation or persistent denial of service through carefully orchestrated concurrent table modification operations.