Bug 2449572 (CVE-2026-23274)

Summary: CVE-2026-23274 kernel: netfilter: xt_IDLETIMER: reject rev0 reuse of ALARM timer labels
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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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 netfilter: xt_IDLETIMER module. This vulnerability occurs when revision 0 rules attempt to reuse a timer label previously created by revision 1 with alarm timer semantics. This action can lead to calling mod_timer() on an uninitialized timer list. A local attacker could potentially trigger debug object warnings and, under certain configurations, cause a kernel panic, leading to a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-03-20 09:03:22 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: xt_IDLETIMER: reject rev0 reuse of ALARM timer labels

IDLETIMER revision 0 rules reuse existing timers by label and always call
mod_timer() on timer->timer.

If the label was created first by revision 1 with XT_IDLETIMER_ALARM,
the object uses alarm timer semantics and timer->timer is never initialized.
Reusing that object from revision 0 causes mod_timer() on an uninitialized
timer_list, triggering debugobjects warnings and possible panic when
panic_on_warn=1.

Fix this by rejecting revision 0 rule insertion when an existing timer with
the same label is of ALARM type.
Comment 1 Alexander B 2026-03-20 12:14:04 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026032034-CVE-2026-23274-ba1d@gregkh/T