Linux kernel TCP UAF in inet_opt handling
CVE-2026-98432 Published on October 15, 2026
ipv4: free inet_opt and ireq_opt after an RCU grace period
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.
Products Associated with CVE-2026-98432
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Affected Versions
Linux:- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below b3b027ef0cd322bfa839b9aaf5b27551eea54cf6 is affected.
- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below 95a8c8fa9f27dce64c40c41c062de7728bf34ab5 is affected.
- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below 89b5b1eb7d633c33832b7ff2c02e19a144705036 is affected.
- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below 742f73df544e03744f2981c467d6542fe8172a2a is affected.
- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below 11a03ce3c4a62d84c10ccdfe47f8075006498568 is affected.
- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below a47406c769f72c070386985488f1c4d057df86b2 is affected.
- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below 26d4c36d318cffbbd160884a0e4cec0da4da4936 is affected.
- Version 079096f103faca2dd87342cca6f23d4b34da8871 and below e3f33b0a1d89d738e2b913dab519226eaf76e15b is affected.
- Version 4.4 is affected.
- Before 4.4 is unaffected.
- Version 5.10.272, <= 5.10.* is unaffected.
- Version 5.15.223, <= 5.15.* is unaffected.
- Version 6.1.190, <= 6.1.* is unaffected.
- Version 6.6.159, <= 6.6.* is unaffected.
- Version 6.12.113, <= 6.12.* is unaffected.
- Version 6.18.56, <= 6.18.* is unaffected.
- Version 7.2.10, <= 7.2.* is unaffected.
- Version 7.3-rc7, <= * is unaffected.