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Predictable Exact Value from Previous Values The advisory has been revoked - it doesn't affect any version of package rv  (opens in a new tab)

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EPSS
0.31% (23rd percentile)

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  • Snyk IDSNYK-RHEL10-RV-18490822
  • published1 Aug 2026
  • disclosed19 Jul 2026
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Introduced: 19 Jul 2026

CVE-2026-64024  (opens in a new tab)
CWE-342  (opens in a new tab)

Amendment

The Red Hat security team deemed this advisory irrelevant for RHEL:10.

NVD Description

Note: Versions mentioned in the description apply only to the upstream rv package and not the rv package as distributed by RHEL.

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%