CVE-2026-74624 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_conntrack: defer invalid log until after unlock
TCP and SCTP conntrack paths can emit invalid-packet logs while ct->lock is still held.
When invalid logging is routed to nfnetlink_log and conntrack export is enabled, the log path can re-enter conntrack netlink glue and dump the same conntrack again. Protocol attribute dumping may take ct->lock, so logging while holding that lock can deadlock.
Defer the TCP invalid logs by storing only the minimal log context while ct->lock is held and emitting the log after unlocking. Also make the TCP timeout-lowering invalid path return whether a log is needed, then emit that log after unlocking.
Do the same for the SCTP invalid state-transition log that can be reached while ct->lock is held.
Add a lockdep assertion to nf_ct_l4proto_log_invalid() so future callers that log invalid conntracks while holding ct->lock are caught outside TCP and SCTP as well.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel netfilter subsystem, specifically the connection tracking component known as nf_conntrack, contained a concurrency vulnerability related to lock ordering and re-entrant logging operations. This issue primarily affected the handling of invalid packets within the Transmission Control Protocol (TCP) and Stream Control Transport Protocol (SCTP) conntrack paths. Under specific conditions where invalid packet logging was configured via nfnetlink_log with connection tracking export enabled, the system could encounter a deadlock scenario. The root cause lies in the fact that when an invalid packet is detected, the kernel attempted to emit a log entry while still holding the ct->lock, which is a spinlock protecting the conntrack structure. This lock acquisition pattern created a potential for re-entrancy issues where the logging mechanism itself required accessing connection tracking data structures protected by the same lock it was already holding or attempting to acquire again through nested calls in the netlink glue code.
The operational impact of this vulnerability is significant, as it can lead to system hangs or kernel panics due to deadlock conditions. When nfnetlink_log processes a log message that triggers conntrack export functionality, it may invoke functions that attempt to dump connection tracking information. These dumping operations often require acquiring the ct->lock to safely read protocol attributes and state data. If this acquisition occurs while the original invalid packet processing routine still holds the lock, a classic deadlock situation arises where two execution contexts wait indefinitely for each other to release resources. This not only disrupts network connectivity monitoring but can also destabilize the entire kernel if the deadlock persists long enough to trigger watchdog timeouts or force emergency reboots.
The resolution involves restructuring how invalid packet logs are generated in both TCP and SCTP conntrack modules. Instead of performing logging operations while holding the ct->lock, the fix defers these actions until after the lock is released. For TCP connections, this means storing only minimal log context information within the critical section protected by the lock and then emitting the actual log message once the lock has been unlocked. Additionally, for cases involving timeout lowering due to invalid states, the code now returns a flag indicating whether logging is required, allowing the caller to handle the logging outside of the locked region. A similar approach was applied to SCTP protocol handling to address its specific state-transition logging paths that were susceptible to the same deadlock pattern.
To prevent future regressions and ensure maintainability, developers added a lockdep assertion within the nf_ct_l4proto_log_invalid function. Lockdep is a kernel debugging feature that tracks lock dependencies at runtime and can detect potential deadlocks before they occur in production environments. By asserting that ct->lock must not be held when invoking this logging routine, any future code changes or new protocol implementations that inadvertently attempt to log invalid conntracks while holding the lock will trigger an immediate warning during testing phases. This proactive measure aligns with best practices for kernel concurrency safety and helps maintain the integrity of synchronization primitives across different network protocols.
From a vulnerability classification perspective, this issue corresponds to CWE-833, Deadlock, as it involves improper handling of resource locks leading to indefinite blocking. In terms of attack vectors or operational impact models like MITRE ATT&CK, while not directly exploitable for remote code execution, such kernel deadlocks can be leveraged in Denial of Service (DoS) attacks by triggering the specific packet conditions that cause the lock contention. Security administrators should ensure their Linux kernels are updated to include this patch, particularly if they rely heavily on nfnetlink_log and conntrack export features for network monitoring or intrusion detection systems. Regular kernel updates and applying vendor security patches remain the primary mitigation strategy against such concurrency flaws in operating system components.