Linux Kernel up to 7.1.4 nf_conntrack_expect nf_ct_remove_expectations race condition

Summaryinfo

A vulnerability has been found in Linux Kernel up to 7.1.4 and classified as very critical. This issue affects the function nf_ct_remove_expectations of the component nf_conntrack_expect. Performing a manipulation results in race condition. This vulnerability is cataloged as CVE-2026-80668. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.1.4. It has been classified as very critical. This affects the function nf_ct_remove_expectations of the component nf_conntrack_expect. The manipulation with an unknown input leads to a race condition vulnerability. CWE is classifying the issue as CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_expect: use conntrack GC to reap expectations This patch replaces the timer API by GC worker approach for expectations, as it already happened in many other subsystems. Use the existing conntrack GC worker to iterate over the local list of expectations in the master conntrack to reap expired expectations. Check IPS_HELPER_BIT to run GC for expectations, set it on for nft_ct expectation which nevers sets it. Hold the expectation spinlock while iterating over the master conntrack expectation list to synchronize with nf_ct_remove_expectations(). This also performs runtime packet path garbage collection through the expectation insertion and lookup functions while walking over one of the chains of the global expectation hashtables. Unconfirmed conntrack entries are skipped since ct->ext can be reallocated and dying are skipped since those will be gone soon. Set on IPS_HELPER_BIT if the helper ct extension is added, then the new GC worker does not need to bump the ct refcount to check if the ct->ext helper is available. This removes the extra bump on the refcount for expectation timers, this allows to remove several nf_ct_expect_put() calls after the unlink, after this update only refcount remains at 1 while on the expectation hashes. This patch implicitly addresses a race with the existing timer API allowing an expectation to access a stale exp->master pointer which has been already released when expectation removal loses races with an expiring timer, ie. timer_del() reporting false. Add a new NF_CT_EXPECT_DEAD flag to reap this expectation via GC. This is needed by nf_conntrack_unexpect_related() which is called in error paths to invalidate newly created expectations that has been added into the hashes. These expectactions cannot be inmediately released as GC or nf_ct_remove_expectations() could race to make it. On expectation insert, the runtime GC reaps stale expectations before checking the expectation limit set by policy. Set current timestamp in nf_ct_expect_alloc(), then add the expectation policy timeout (or custom timeout specified added on top of this) to specify the expectation lifetime.

The advisory is shared at git.kernel.org. This vulnerability is uniquely identified as CVE-2026-80668 since 08/26/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/28/2026).

Upgrading to version 7.1.5 eliminates this vulnerability. Applying the patch 7ec786f4230c2a9b2eaf97a2d45368933b49d2b2/b8b09dc2bf35a00d4e0556b5d6308c7b917ebda2 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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