CVE-2026-98432
Received Received - Intake

Use-After-Free in Linux Kernel TCP/IP Stack

Publication date: 2026-10-15

Last updated on: 2026-10-15

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: ipv4: free inet_opt and ireq_opt after an RCU grace period tcp_v4_syn_recv_sock() transfers ownership of ireq->ireq_opt to the child socket (newinet->inet_opt) without copying it. Another cpu can concurrently process a retransmitted SYN for the same request socket, and send a SYNACK from tcp_check_req(). tcp_v4_send_synack() and inet_csk_route_req() read ireq->ireq_opt under rcu_read_lock() only, and ip_build_and_send_pkt() and ip_options_build() then read opt->optlen twice. Note that the SYNACK timer itself is not an issue: it holds a reference on its request socket, and inet_csk_reqsk_queue_drop() calls timer_delete_sync() before the child can be freed. Since commit 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table"), request sockets are processed without holding the listener lock, so nothing prevents the child socket from being freed while the SYNACK is still being built. TCP child sockets do not have SOCK_RCU_FREE, and inet_sock_destruct() frees inet_opt with a plain kfree(), leading to a use-after-free in ip_options_build(). A similar issue exists with request socket migration (net.ipv4.tcp_migrate_req=1, or a BPF_SK_REUSEPORT_SELECT_OR_MIGRATE program). reqsk_timer_handler() clones the request socket with inet_reqsk_clone(), so that the old request socket and its clone share the same ireq_opt, then reqsk_migrate_reset() clears the pointer in the old one. Another cpu holding a reference on the old request socket can still be using these options (sending a SYNACK, or creating a child in tcp_v4_syn_recv_sock()) when the clone is freed, and tcp_v4_reqsk_destructor() also uses a plain kfree(). Readers already use RCU, and other paths replacing inet_opt (do_ip_setsockopt(), cipso_v4_sock_setattr()...) already use kfree_rcu(). Use kfree_rcu() in inet_sock_destruct() and tcp_v4_reqsk_destructor() as well. IPv6 is not affected by the first issue, because tcp_v6_syn_recv_sock() duplicates the options. tcp_v6_reqsk_destructor() has the same migration issue with ipv6_opt, which is only set by CALIPSO. This will be addressed in a separate patch.

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Meta Information

Published
2026-10-15
Last Modified
2026-10-15
Generated
2026-10-15
AI Q&A
2026-10-15
EPSS Evaluated
N/A
NVD
CVE-2026-98432
EUVD
EUVD-2026-102025

Affected Vendors & Products

Showing 9 associated CPEs
Vendor Product Version / Range
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 079096f103faca2dd87342cca6f23d4b34da8871
Linux Linux 4.4

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Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a use-after-free vulnerability in the Linux kernel's IPv4 networking stack. It occurs when a TCP child socket is freed while another CPU is still using its inet_opt or ireq_opt structures. The issue arises because the child socket inherits these structures without copying them, and the original structures are freed with a plain kfree() instead of kfree_rcu(). This leads to a use-after-free when another CPU tries to access the freed memory while building a SYNACK packet.

Detection Guidance

This vulnerability involves a use-after-free issue in the Linux kernel's TCP/IP stack, specifically related to IPv4 socket options handling. Detection requires kernel-level inspection and may not be straightforward with standard network commands. Focus on monitoring kernel logs for memory corruption errors or crashes related to TCP/IP processing. Check for kernel oops messages or segmentation faults in system logs that may indicate use-after-free conditions.

Impact Analysis

This vulnerability could allow an attacker to cause a denial-of-service (system crash) or potentially execute arbitrary code with kernel privileges. It affects systems running vulnerable Linux kernel versions, enabling remote attackers to trigger the flaw via network traffic. Systems without IPv4 networking or with specific kernel configurations may be less affected.

Mitigation Strategies

Apply the kernel patch that addresses this issue by using kfree_rcu() instead of kfree() in inet_sock_destruct() and tcp_v4_reqsk_destructor(). Update to a Linux kernel version that includes the fix. If immediate patching is not possible, consider disabling IPv4 TCP options or restricting network services using vulnerable TCP features until the patch is applied.

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