Bug 2517027 (CVE-2026-74492)

Summary: CVE-2026-74492 kernel: netfilter: ipset: do not update comments from kernel-side hash adds
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
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's netfilter ipset component. During an ipset hash table resize operation, a race condition can occur where a packet-side add attempts to update a comment. This can lead to a stale pointer being dereferenced, resulting in a kernel crash and a Denial of Service (DoS) for the affected system. A remote attacker could potentially exploit this vulnerability by sending specially crafted network packets.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-15 12:45:20 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: ipset: do not update comments from kernel-side hash adds

mtype_resize() copies comment pointers with memcpy(), not the comment
objects themselves. During the window after an entry has been copied but
before the table swap and backlog replay, the old table is still
published for packet-side updates while the replacement-table entry
already holds the same ip_set_comment_rcu pointer.

If xt_SET --add-set ... --exist hits that old entry in this window,
mtype_add() calls ip_set_init_comment() even though packet-side adds
carry no comment payload. That call frees the shared comment through the
old entry, so the replacement-table entry now holds a stale pointer.
When the queued add is replayed on the new table, mtype_add() calls
ip_set_init_comment() again and strlen() dereferences the stale pointer.

Fix this in mtype_add() by skipping ip_set_init_comment() when
ext->target marks a packet-side add. Userspace adds still update
comments, while packet-side adds can no longer free comment storage
shared with a resize copy.
Comment 1 Mauro Matteo Cascella 2026-08-20 18:28:05 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081539-CVE-2026-74492-a089@gregkh/T