CVE-2025-40186High· 8.1▾ TwilightIn the Linux kernel, the following vulnerability has been resolved: tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request(). syzbot reported the splat below in tcp_conn_request(). [0] If a listener is close()d while a TFO socket…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 44.6 · likelihood 0.1 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
Last analysed / modified upstream
0.6%
In the Linux kernel, the following vulnerability has been resolved:
tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request().
syzbot reported the splat below in tcp_conn_request(). [0]
If a listener is close()d while a TFO socket is being processed in tcp_conn_request(), inet_csk_reqsk_queue_add() does not set reqsk->sk and calls inet_child_forget(), which calls tcp_disconnect() for the TFO socket.
After the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(), where reqsk_put() is called due to !reqsk->sk.
Then, reqsk_fastopen_remove() in tcp_conn_request() decrements the last req->rsk_refcnt and frees reqsk, and __reqsk_free() at the drop_and_free label causes the refcount underflow for the listener and double-free of the reqsk.
Let's remove reqsk_fastopen_remove() in tcp_conn_request().
Note that other callers make sure tp->fastopen_rsk is not NULL.
[0]: refcount_t: underflow; use-after-free. WARNING: CPU: 12 PID: 5563 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28) Modules linked in: CPU: 12 UID: 0 PID: 5563 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:refcount_warn_saturate (lib/refcount.c:28) Code: ab e8 8e b4 98 ff 0f 0b c3 cc cc cc cc cc 80 3d a4 e4 d6 01 00 75 9c c6 05 9b e4 d6 01 01 48 c7 c7 e8 df fb ab e8 6a b4 98 ff <0f> 0b e9 03 5b 76 00 cc 80 3d 7d e4 d6 01 00 0f 85 74 ff ff ff c6 RSP: 0018:ffffa79fc0304a98 EFLAGS: 00010246 RAX: d83af4db1c6b3900 RBX: ffff9f65c7a69020 RCX: d83af4db1c6b3900 RDX: 0000000000000000 RSI: 00000000ffff7fff RDI: ffffffffac78a280 RBP: 000000009d781b60 R08: 0000000000007fff R09: ffffffffac6ca280 R10: 0000000000017ffd R11: 0000000000000004 R12: ffff9f65c7b4f100 R13: ffff9f65c7d23c00 R14: ffff9f65c7d26000 R15: ffff9f65c7a64ef8 FS: 00007f9f962176c0(0000) GS:ffff9f65fcf00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000000180 CR3: 000000000dbbe006 CR4: 0000000000372ef0 Call Trace: <IRQ> tcp_conn_request (./include/linux/refcount.h:400 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 ./include/net/sock.h:1965 ./include/net/request_sock.h:131 net/ipv4/tcp_input.c:7301) tcp_rcv_state_process (net/ipv4/tcp_input.c:6708) tcp_v6_do_rcv (net/ipv6/tcp_ipv6.c:1670) tcp_v6_rcv (net/ipv6/tcp_ipv6.c:1906) ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:438) ip6_input (net/ipv6/ip6_input.c:500) ipv6_rcv (net/ipv6/ip6_input.c:311) __netif_receive_skb (net/core/dev.c:6104) process_backlog (net/core/dev.c:6456) __napi_poll (net/core/dev.c:7506) net_rx_action (net/core/dev.c:7569 net/core/dev.c:7696) handle_softirqs (kernel/softirq.c:579) do_softirq (kernel/softirq.c:480) </IRQ>
Linux >= 7ec092a91ff351dcde89c23e795b73a328274db6 < e359b742eac1eac75cff4e38ee2e8cea492acd9bLinux >= a4378dedd6e07e62f2fccb17d78c9665718763d0 < ff6a8883f96a5bc74241ce5b3d431a6dcfa2124dLinux >= 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 < eb85ad5f23268d64b037bfb545cbcba3752f90c7Linux >= 17d699727577814198d744d6afe54735c6b54c99 < 643a94b0cf767325e953591c212be2eb826b9d7fLinux >= dfd06131107e7b699ef1e2a24ed2f7d17c917753 < 422c1c173c39bbbae1e0eaaf8aefe40b2596233bLinux >= fa4749c065644af4db496b338452a69a3e5147d9 < c11ace909e873118295e9eb22dc8c58b0b50eb32Linux >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 64dc47a13aa3d9daf7cec29b44dca8e22a6aea15Linux >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 2e7cbbbe3d61c63606994b7ff73c72537afe2e1cLinux ae313d14b45eca7a6bb29cb9bf396d977e7d28fbLinux >= 5.4.300 < 5.4.301Linux >= 5.10.245 < 5.10.246Linux >= 5.15.194 < 5.15.195Linux >= 6.1.154 < 6.1.157Linux >= 6.6.108 < 6.6.113Linux >= 6.12.49 < 6.12.54Linux >= 6.16.9 < 6.17Linux 6.17Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
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