Bug 2521430 (CVE-2026-74696)

Summary: CVE-2026-74696 kernel: tcp: fix TFO max_qlen accounting across reuseport migration
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
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 TCP Fast Open (TFO) implementation. During SO_REUSEPORT listener migration, the system incorrectly accounts for pending TCP Fast Open requests. This can lead to a Denial of Service (DoS) by allowing an excessive number of Fast Open requests, potentially exhausting system resources.
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Description OSIDB Bzimport 2026-08-22 15:45:13 UTC 
In the Linux kernel, the following vulnerability has been resolved:

tcp: fix TFO max_qlen accounting across reuseport migration

A listener's TCP_FASTOPEN max_qlen stops being accurate and lets through
far more pending Fast Open requests than it was configured for.

This only shows up with SO_REUSEPORT listener migration, where closing a
listener hands its still-pending TFO children over to a surviving one.

fastopenq.qlen is charged in tcp_fastopen_create_child() when the child
is created and uncharged in reqsk_fastopen_remove() when the handshake
completes.  The uncharge follows rsk_listener of the request the child
points at, and inet_reqsk_clone() has repointed the child at a new
request owned by the new listener, so the ++ and the -- land on two
different sockets.  The new listener's qlen drifts negative and its
limit no longer binds.

Charge the new listener during migration, like reqsk_queue_migrated()
already does for queue->young and queue->qlen.
Comment 1 Keith Grant 2026-08-24 17:21:16 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082234-CVE-2026-74696-3187@gregkh/T