CVE-2026-98432: ipv4: free inet_opt and ireq_opt after an RCU grace period
Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.
Generated by VEDAS. Scores as of 2026-11-01 19:19 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.
What it is
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.
Description quoted from the CVE record (assigned by Linux, published 2026-10-15).
How it can be exploited
Exploitable over the network with low attack complexity needing no privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Public exploit evidence (Exploit Observer)
Exploit Observer evidence for this CVE has not been fetched yet.
Live scores
- EPSS
- 0.005
low predicted chance of attack - VEDAS
- 0.969
strong exploit evidence - On CISA KEV
- Not listed
- Detection rule
- None yet
Who is affected
| Product | Affected | Not affected |
|---|---|---|
| Linux Linux | from 079096f103fa before b3b027ef0cd3 (git commit) from 079096f103fa before 95a8c8fa9f27 (git commit) from 079096f103fa before 89b5b1eb7d63 (git commit) from 079096f103fa before 742f73df544e (git commit) from 079096f103fa before 11a03ce3c4a6 (git commit) from 079096f103fa before a47406c769f7 (git commit) from 079096f103fa before 26d4c36d318c (git commit) from 079096f103fa before e3f33b0a1d89 (git commit) | Not stated |
| Linux Linux | version 4.4 | 0 is not affected (up to 4.4); 5.10.272 is not affected; 5.15.223 is not affected; 6.1.190 is not affected |
Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.
How to fix it
No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.
How to detect it
There is no open VEDAS detection rule for this bug yet. It is listed on the detection gaps page if CISA has confirmed attacks.
Advisories on this CVE
- Linux kernel CVE-2026-98432: IPv4 TCP handshake use-after-free, with an AI-built remote root exploit (full advisory)
- Linux kernel: IPv4 TCP handshake use-after-free, Claude-built remote root exploit (CVE-2026-98432) (27 Oct 2026)
References
Other references
- https://git.kernel.org/stable/c/b3b027ef0cd322bfa839b9aaf5b27551eea54cf6
- https://git.kernel.org/stable/c/95a8c8fa9f27dce64c40c41c062de7728bf34ab5
- https://git.kernel.org/stable/c/89b5b1eb7d633c33832b7ff2c02e19a144705036
- https://git.kernel.org/stable/c/742f73df544e03744f2981c467d6542fe8172a2a
- https://git.kernel.org/stable/c/11a03ce3c4a62d84c10ccdfe47f8075006498568
- https://git.kernel.org/stable/c/a47406c769f72c070386985488f1c4d057df86b2
- https://git.kernel.org/stable/c/26d4c36d318cffbbd160884a0e4cec0da4da4936
- https://git.kernel.org/stable/c/e3f33b0a1d89d738e2b913dab519226eaf76e15b
- http://www.openwall.com/lists/oss-security/2026/10/30/1
- http://www.openwall.com/lists/oss-security/2026/10/30/6
- http://www.openwall.com/lists/oss-security/2026/10/31/5
Other databases
Where this comes from
This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS). Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.
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