CVE-2026-63971 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
sctp: fix race between sctp_wait_for_connect and peeloff
sctp_wait_for_connect() drops and re-acquires the socket lock while waiting for the association to reach ESTABLISHED state. During this window, another thread can peeloff the association to a new socket via getsockopt(SCTP_SOCKOPT_PEELOFF), changing asoc->base.sk. After re-acquiring the old socket lock, sctp_wait_for_connect() returns success without noticing the migration — the caller then accesses the association under the wrong lock in sctp_datamsg_from_user().
Add the same sk != asoc->base.sk check that sctp_wait_for_sndbuf() already has, returning an error if the association was migrated while we slept.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability exists within the Stream Control Transmission Protocol implementation of the Linux kernel, specifically addressing a race condition between the sctp_wait_for_connect function and the peeloff operation. The flaw occurs when a socket lock is dropped and re-acquired during connection establishment, creating a temporal window where concurrent operations can modify the association's socket reference. The sctp_wait_for_connect function temporarily releases the socket lock while waiting for an association to reach the ESTABLISHED state, allowing another thread to execute the peeloff operation through getsockopt with SCTP_SOCKOPT_PEELOFF option. This operation migrates the association from its original socket to a new socket, effectively changing asoc->base.sk from the old socket reference to the new one. When sctp_wait_for_connect re-acquires the original socket lock, it incorrectly assumes the association is still associated with the same socket and returns success without detecting that the migration has occurred.
The technical impact of this race condition manifests when the calling function subsequently accesses the association through sctp_datamsg_from_user(), attempting to operate on an association that has been migrated to a different socket context. This creates a fundamental mismatch between the lock context and the association's actual socket reference, leading to potential memory corruption, data inconsistency, and undefined behavior. The vulnerability is particularly dangerous because it operates silently without error reporting, allowing corrupted state transitions to propagate through the system. This issue directly relates to CWE-362, which describes race conditions where multiple threads access shared resources concurrently without proper synchronization mechanisms, and aligns with ATT&CK technique T1059.003 for privilege escalation through kernel-level manipulation.
The operational impact extends beyond simple data corruption to potentially enable privilege escalation attacks or system instability. An attacker could exploit this vulnerability by carefully orchestrating concurrent connection establishment and peeloff operations to force the system into an inconsistent state where association metadata points to incorrect socket contexts. The fix implements a defensive check similar to that already present in sctp_wait_for_sndbuf(), specifically adding a validation that compares the current socket reference with asoc->base.sk before proceeding. This check ensures that if the association has been migrated during the wait period, the function returns an error rather than continuing with potentially invalid state. The mitigation strategy prevents the silent failure mode by explicitly detecting socket migration and aborting the connection establishment process when such a condition is detected. This approach aligns with established kernel security practices for handling concurrent access patterns and demonstrates the importance of maintaining consistency between lock contexts and resource references. The solution follows the principle of fail-fast behavior, ensuring that inconsistent state transitions are immediately flagged rather than allowed to propagate through subsequent operations.
The vulnerability represents a classic example of improper synchronization in kernel space where temporal consistency is not maintained across concurrent operations. The race condition occurs because sctp_wait_for_connect() does not account for the possibility that the association it was monitoring might have been moved to a different socket during its wait period, creating a scenario where lock and reference consistency are violated. This flaw affects systems running Linux kernels with SCTP support, particularly those handling high-concurrency network operations or applications utilizing SCTP's peeloff functionality. The vulnerability is classified as moderate to high severity due to its potential for causing system instability and the possibility of exploitation for privilege escalation. System administrators should ensure kernel updates are applied promptly to address this race condition, especially in environments where SCTP-based applications are deployed with concurrent connection handling requirements. The fix demonstrates that maintaining reference consistency during lock transitions is crucial for preventing subtle but dangerous race conditions in kernel networking code.