In the Linux kernel, the following vulnerability has been resolved:
tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction
Blamed commit moved the TIME_WAIT-derived ISN from the skb control
block to a per-CPU variable, assuming the value would always be consumed
by tcp_conn_request() for the same packet that wrote it. That assumption
is violated by multiple drop paths between the producer
(__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer
(tcp_conn_request()):
- min_ttl / min_hopcount check
- xfrm policy check
- tcp_inbound_hash() MD5/AO mismatch
- tcp_filter() eBPF/SO_ATTACH_FILTER drop
- th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN
- psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv()
- tcp_checksum_complete() in tcp_v{4,6}_do_rcv()
- tcp_v{4,6}_cookie_check() returning NULL
When a packet is dropped on any of these paths, tcp_tw_isn is left set.
The next SYN processed on the same CPU then consumes the non zero value in
tcp_conn_request(), receiving a potentially predictable ISN.
This patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu
variable.
Note that tcp_v{4,6}_fill_cb() do not set it.
Very litle impact on overall code size/complexity:
$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7)
Function old new delta
tcp_v6_rcv 3038 3042 +4
tcp_v4_rcv 3035 3039 +4
tcp_conn_request 2938 2923 -15
Total: Before=24436060, After=24436053, chg -0.00%
References
Configurations
Configuration 1 (hide)
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History
29 Oct 2026, 15:55
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://git.kernel.org/stable/c/8bb6aa419b142dcc2680177ecc39c4c38db7fc16 - Patch |
21 Oct 2026, 13:19
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
19 Oct 2026, 21:17
| Type | Values Removed | Values Added |
|---|---|---|
| CWE | CWE-362 |
13 Oct 2026, 15:00
| Type | Values Removed | Values Added |
|---|---|---|
| CWE | CWE-401 | |
| References | () https://git.kernel.org/stable/c/1bbf0ced1d9db73ac7893c2187f3459288603e0d - Patch | |
| References | () https://git.kernel.org/stable/c/4affe063fa56c880cbea8d0bfded0bb80751579d - Patch | |
| References | () https://git.kernel.org/stable/c/e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd - Patch | |
| CPE | cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
|
| First Time |
Linux
Linux linux Kernel |
Information
Published : 2026-07-19 16:17
Updated : 2026-10-29 15:55
NVD link : CVE-2026-64024
Mitre link : CVE-2026-64024
CVE.ORG link : CVE-2026-64024
JSON object : View
Products Affected
linux
- linux_kernel
