Copyright © 2012 Red Hat, Inc. All rights reserved. Important 2026-11-10T18:19:08 kernel: kernel: Denial of Service via race condition in TCP socket lookup 7.5 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H CWE-476

In the Linux kernel, the following vulnerability has been resolved: inet: reject unhashed sockets during established lookups TCP established ehash lookups are lockless. The socket caches involved use SLAB_TYPESAFE_BY_RCU, so memory can be reused before an RCU reader that retained its old address has finished. After a tuple match, __inet_lookup_established() and __inet6_lookup_established() acquire a reference and repeat the tuple check. They do not check whether the new object is hashed. If the address is reused for a socket with the same tuple, the lookup can acquire a reference to the new object and return it while its nulls node is unhashed. A PoC that drives reuse with a SYN cookie request socket reproduced the crash. The new request socket is unhashed and has a NULL rsk_listener. A lookup that had loaded the address of the old request socket acquired the reference published by tcp_get_cookie_sock() and returned the new object. tcp_v4_rcv() then read sk_state through the NULL listener. The resulting crash was: BUG: kernel NULL pointer dereference, address: 0000000000000012 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page ... Oops: Oops: 0000 [#1] SMP NOPTI CPU: 4 UID: 0 PID: 0 Comm: swapper/4 Not tainted 7.3.0-00591-g0e135910deec #1 PREEMPT(lazy) ... RIP: 0010:tcp_v4_rcv+0x44e/0x1280 ... R10: 0000000000000001 R11: 00000000024ca8c0 R12: 0000000000000000 ... CR2: 0000000000000012 CR3: 0000000103d50004 CR4: 0000000000770ef0 ... Call Trace: <IRQ> ? raw_local_deliver+0xae/0x240 ip_protocol_deliver_rcu+0x2d/0x180 ip_local_deliver_finish+0x84/0x100 ip_sublist_rcv_finish+0x5f/0x70 ip_sublist_rcv+0x12a/0x1d0 ip_list_rcv+0xfd/0x130 __netif_receive_skb_list_core+0x223/0x250 netif_receive_skb_list_internal+0x1d2/0x2c0 ? try_fill_recv+0x39/0x7b0 napi_complete_done+0x74/0x170 virtnet_poll+0x445/0x600 __napi_poll+0x27/0x1e0 net_rx_action+0x2fe/0x3b0 handle_softirqs+0xc2/0x2c0 __irq_exit_rcu+0x74/0xd0 common_interrupt+0x7f/0x90 </IRQ> ... Kernel panic - not syncing: Fatal exception in interrupt After taking a reference, check whether the nulls node is unhashed in both IPv4 and IPv6 established lookups. If it is unhashed or the tuple no longer matches, drop the reference and restart the lookup. Lookups racing with the TIME_WAIT hashdance, or with a request being replaced by its child, now restart and find the new socket instead of returning the old one. Request sockets that were never inserted into ehash can have a nonzero refcount, and a stale lookup can hold a transient reference. Therefore, when SYN cookie, Fast Open, and request migration paths fail after setting a nonzero refcount, release the references held by those paths with reqsk_put() instead of freeing the request directly.

A flaw was found in the Linux kernel's TCP networking subsystem. Due to a race condition during lockless socket lookups, recycled socket memory can be accessed before it is properly initialized and hashed. A remote attacker could exploit this issue by generating network traffic that drives socket reuse, triggering a NULL pointer dereference and kernel crash that results in a Denial of Service (DoS).

This vulnerability is rated as an Important impact because an unauthenticated remote attacker can trigger an immediate operating system crash across the network without requiring privileges. In standard Red Hat Enterprise Linux deployments, TCP networking is universally enabled, making any system with active network listeners susceptible to high-volume socket recycling traffic. While this flaw causes a kernel panic that disrupts host availability, it does not allow data alteration or arbitrary code execution. ## 1. Disable SYN cookies This blocks the path where a request socket is reconstructed through a SYN cookie. sudo sysctl -w net.ipv4.tcp_syncookies=0 This setting is managed per network namespace. It has to be applied to "each" container that uses a separate network namespace. Disabling it lowers the protection against SYN floods. ## 2. Serialize to a single RX queue This vulnerability requires different RX contexts to race concurrently. Reducing the RX queues of the interface where external packets come in to one and disabling RPS and RFS can block the race. Red Hat Enterprise Linux 10 Affected kernel Red Hat Enterprise Linux 6 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel-rt Red Hat Enterprise Linux 8 Affected kernel Red Hat Enterprise Linux 8 Affected kernel-rt Red Hat Enterprise Linux 9 Affected kernel Red Hat Enterprise Linux 9 Affected kernel-rt Red Hat OpenShift Container Platform 4 Affected openshift/ose-rhel-coreos-8 Red Hat OpenShift Container Platform 4 Affected openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 Affected openshift/ose-rhel-coreos-10 Red Hat OpenShift Container Platform 5 Affected openshift/ose-rhel-coreos-9 https://www.cve.org/CVERecord?id=CVE-2026-99288 https://nvd.nist.gov/vuln/detail/CVE-2026-99288 https://git.kernel.org/stable/c/8e5172cbd227fae32f3313cba1f3e1b9edb5c4fd https://git.kernel.org/stable/c/d69100340b4cae08d40f898f1b601032403f6be6 https://git.kernel.org/stable/c/eb8a2d156f2c1d862fffdfd1b3432bfbcd939879