Linux Kernel: netfilter IDLETIMER Reuse of ALARM Timer Causing Panic
CVE-2026-23274 Published on March 20, 2026
netfilter: xt_IDLETIMER: reject rev0 reuse of ALARM timer labels
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.
Products Associated with CVE-2026-23274
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Affected Versions
Linux:- Version 68983a354a655c35d3fb204489d383a2a051fda7 and below f5ef97c13165542480a6ffdbe6f09f40bbb7cbf1 is affected.
- Version 68983a354a655c35d3fb204489d383a2a051fda7 and below f228b9ae2a7e84d1153616d8e71c4236cb1f1309 is affected.
- Version 68983a354a655c35d3fb204489d383a2a051fda7 and below 329f0b9b48ee6ab59d1ab72fef55fe8c6463a6cf is affected.
- Version 5.7 is affected.
- Before 5.7 is unaffected.
- Version 6.18.19, <= 6.18.* is unaffected.
- Version 6.19.9, <= 6.19.* is unaffected.
- Version 7.0-rc4, <= * is unaffected.