Bug 2482170 (CVE-2026-45889)

Summary: CVE-2026-45889 kernel: mptcp: do not account for OoO in mptcp_rcvbuf_grow()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Multipath TCP (MPTCP) implementation. This vulnerability occurs due to incorrect accounting for out-of-order (OoO) data in the `mptcp_rcvbuf_grow()` function. A subtle and very unlikely race condition could lead to a divide-by-zero error, potentially causing a system crash (Denial of Service).
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Description OSIDB Bzimport 2026-05-27 15:14:37 UTC 
In the Linux kernel, the following vulnerability has been resolved:

mptcp: do not account for OoO in mptcp_rcvbuf_grow()

MPTCP-level OoOs are physiological when multiple subflows are active
concurrently and will not cause retransmissions nor are caused by
drops.

Accounting for them in mptcp_rcvbuf_grow() causes the rcvbuf slowly
drifting towards tcp_rmem[2].

Remove such accounting. Note that subflows will still account for TCP-level
OoO when the MPTCP-level rcvbuf is propagated.

This also closes a subtle and very unlikely race condition with rcvspace
init; active sockets with user-space holding the msk-level socket lock,
could complete such initialization in the receive callback, after that the
first OoO data reaches the rcvbuf and potentially triggering a divide by
zero Oops.
Comment 1 Keith Grant 2026-05-28 02:56:55 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052717-CVE-2026-45889-b9d5@gregkh/T