Bug 2454866 (CVE-2026-23437)

Summary: CVE-2026-23437 kernel: net: shaper: protect late read accesses to the hierarchy
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel's `net: shaper` module. This vulnerability arises from a missing liveness check during Netlink operations when a network device (netdev) is referenced and subsequently accessed. If the netdev is unregistered before the access, it can lead to a use-after-free condition. This could allow an attacker to cause a denial of service.
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Description OSIDB Bzimport 2026-04-03 16:05:06 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net: shaper: protect late read accesses to the hierarchy

We look up a netdev during prep of Netlink ops (pre- callbacks)
and take a ref to it. Then later in the body of the callback
we take its lock or RCU which are the actual protections.

This is not proper, a conversion from a ref to a locked netdev
must include a liveness check (a check if the netdev hasn't been
unregistered already). Fix the read cases (those under RCU).
Writes needs a separate change to protect from creating the
hierarchy after flush has already run.
Comment 1 Jon Moroney 2026-04-03 16:58:49 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026040312-CVE-2026-23437-9787@gregkh/T