CVE-2026-43116
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Race Condition in Linux Kernel Netfilter ctnetlink

Publication date: 2026-05-06

Last updated on: 2026-05-06

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: ensure safe access to master conntrack Holding reference on the expectation is not sufficient, the master conntrack object can just go away, making exp->master invalid. To access exp->master safely: - Grab the nf_conntrack_expect_lock, this gets serialized with clean_from_lists() which also holds this lock when the master conntrack goes away. - Hold reference on master conntrack via nf_conntrack_find_get(). Not so easy since the master tuple to look up for the master conntrack is not available in the existing problematic paths. This patch goes for extending the nf_conntrack_expect_lock section to address this issue for simplicity, in the cases that are described below this is just slightly extending the lock section. The add expectation command already holds a reference to the master conntrack from ctnetlink_create_expect(). However, the delete expectation command needs to grab the spinlock before looking up for the expectation. Expand the existing spinlock section to address this to cover the expectation lookup. Note that, the nf_ct_expect_iterate_net() calls already grabs the spinlock while iterating over the expectation table, which is correct. The get expectation command needs to grab the spinlock to ensure master conntrack does not go away. This also expands the existing spinlock section to cover the expectation lookup too. I needed to move the netlink skb allocation out of the spinlock to keep it GFP_KERNEL. For the expectation events, the IPEXP_DESTROY event is already delivered under the spinlock, just move the delivery of IPEXP_NEW under the spinlock too because the master conntrack event cache is reached through exp->master. While at it, add lockdep notations to help identify what codepaths need to grab the spinlock.
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Meta Information
Published
2026-05-06
Last Modified
2026-05-06
Generated
2026-05-07
AI Q&A
2026-05-06
EPSS Evaluated
N/A
NVD
CVE-2026-43116
EUVD
EUVD-2026-27641
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux_kernel linux_kernel *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability exists in the Linux kernel's netfilter component, specifically in the ctnetlink subsystem that manages connection tracking expectations.

The issue arises because holding a reference on the expectation object alone is not sufficient to ensure the master conntrack object remains valid. The master conntrack object can be removed, making the reference (exp->master) invalid and potentially leading to unsafe access.

To fix this, the patch extends the locking mechanism (nf_conntrack_expect_lock) to ensure safe access to the master conntrack object by serializing access and holding proper references during operations such as adding, deleting, and getting expectations.

The fix involves expanding the spinlock sections to cover expectation lookups and moving certain operations outside the spinlock to maintain kernel memory allocation safety. It also includes delivering certain events under the spinlock and adding lock dependency annotations to help identify necessary locking paths.


How can this vulnerability impact me? :

This vulnerability can lead to unsafe access to kernel data structures related to connection tracking in the Linux kernel.

If exploited or triggered, it could cause kernel instability or crashes due to accessing invalid or freed memory (use-after-free conditions). This may result in denial of service or potentially other unpredictable behavior in systems relying on netfilter connection tracking.


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