Bug 2536252 (CVE-2026-90061)

Summary: CVE-2026-90061 kernel: netfilter: nf_tables: skip double clone set expressions on element insert
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: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, 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 netfilter nf_tables component of the Linux kernel. When new elements are inserted into a set without providing override expressions, a double cloning of existing set expressions occurs. This can lead to a module reference count imbalance, potentially causing system instability or a denial of service (DoS) condition.
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Description OSIDB Bzimport 2026-09-17 17:07:33 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_tables: skip double clone set expressions on element insert

Both the dynset and newsetelem path clone the existing set expressions
when setting set element expressions if no override expressions are
provided. This results in a double clone, once to clone the template set
expressions then another clone on the new element. Add a flag to
annotate if userspace provides a override expression (ie. expression of
the same type of the set but different configuration), otherwise borrow
the existing expression from the set. Add conditionals to release
expression iif they represent an override. Use this new override_exprs
flag to dump the dynset expression override to userspace.

This simplifies the existing logic and it also fixes a bug with the
connlimit expression which results in a module refcount imbalance
WARNING splat when resorting on the default set expressions.
Comment 1 Keith Grant 2026-09-22 15:46:26 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-90061.mbox