CVE-2026-68335 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
rds: drop incoming messages that cross network namespace boundaries
rds_find_bound() looks up the destination socket using a global rhashtable keyed solely on (addr, port, scope_id). Network namespaces are not part of the key, so a sender in netns A can deliver an incoming message (inc) to a socket that lives in a different netns B.
When this happens, inc->i_conn points to an rds_connection whose c_net is netns A, but the receiving rs lives in netns B. Once the child process that created netns A exits, cleanup_net() calls rds_loop_exit_net() -> rds_loop_kill_conns() -> rds_conn_destroy(), freeing that connection. If the survivor socket in netns B still holds the inc, any subsequent dereference of inc->i_conn is a use-after-free.
There are two dangerous sites in rds_clear_recv_queue(): 1. inc->i_conn->c_lcong (offset 88 of freed rds_connection, size 200) read via rds_recv_rcvbuf_delta() -- confirmed by KASAN. 2. inc->i_conn->c_trans->inc_free(inc) (function pointer at offset 80) called via rds_inc_put() when the inc refcount reaches zero -- same race window, potential call-through-freed-object primitive.
The bug is reachable from unprivileged user namespaces (CLONE_NEWUSER + CLONE_NEWNET), available since Linux 3.8.
Fix this by rejecting the delivery in rds_recv_incoming() when the socket returned by rds_find_bound() belongs to a different network namespace than the connection that carried the message. Use the existing rds_conn_net() / sock_net() helpers and net_eq() for the comparison.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability described represents a critical use-after-free condition in the Linux kernel's Reliable Datagram Sockets (RDS) implementation that stems from improper network namespace isolation during message delivery. This flaw allows an attacker to potentially execute arbitrary code by exploiting a race condition between network namespace cleanup and socket reference handling, specifically within the rds subsystem that manages communication between nodes in high-performance computing environments.
The technical root cause lies in the rds_find_bound() function which utilizes a global rhashtable for socket lookups without incorporating network namespace information into the hash key structure. This design flaw means that when a sender operating within network namespace A attempts to deliver a message to a socket located in network namespace B, the lookup mechanism will incorrectly return the target socket despite the namespace mismatch. The connection structure (rds_connection) associated with the incoming message maintains a reference to namespace A through its c_net field, while the receiving socket exists in namespace B, creating a fundamental architectural inconsistency.
The operational impact of this vulnerability becomes apparent during the cleanup process that occurs when a network namespace is destroyed. When the parent process that created namespace A terminates, the kernel executes cleanup_net() which triggers rds_loop_exit_net() followed by rds_loop_kill_conns() and ultimately rds_conn_destroy(). This sequence frees the connection structure while leaving references to it still active within the socket in namespace B. Any subsequent dereference of inc->i_conn results in a use-after-free condition that can be exploited for privilege escalation or system compromise.
Two specific dangerous memory access patterns have been identified during analysis of the rds_clear_recv_queue() function, both occurring within the same race window and presenting distinct exploitation vectors. The first involves reading from inc->i_conn->c_lcong at offset 88 (size 200 bytes) through the rds_recv_rcvbuf_delta() function, which has been confirmed by KASAN memory error detection. The second represents a more severe primitive involving a function pointer call at offset 80 via inc->i_conn->c_trans->inc_free(inc) when the reference count reaches zero, creating a potential call-through-freed-object scenario that can be leveraged for code execution.
This vulnerability is particularly concerning because it can be triggered from unprivileged user namespaces, making exploitation significantly more accessible than traditional kernel vulnerabilities. The CLONE_NEWUSER and CLONE_NEWNET system calls have been available since Linux 3.8, providing attackers with legitimate means to create isolated network environments where they can establish the required conditions for triggering this race condition without requiring elevated privileges.
The fix implemented addresses the core architectural issue by introducing explicit namespace validation during message delivery in rds_recv_incoming(). The solution employs existing kernel infrastructure including rds_conn_net() and sock_net() helpers along with net_eq() comparison functions to ensure that incoming messages are only delivered to sockets within the same network namespace as the connection that carried them. This approach follows established security patterns for namespace isolation and prevents the cross-namespace message delivery that enables the use-after-free condition.
This vulnerability aligns with CWE-416 (Use After Free) and CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization), and maps to ATT&CK techniques involving privilege escalation through kernel exploits and code injection. The remediation approach demonstrates proper kernel security practices by implementing defensive programming measures that prevent namespace boundary violations while maintaining the functional integrity of the RDS communication subsystem essential for high-performance computing environments.