GHSA-FPGW-998R-PG47
Vulnerability from github – Published: 2026-08-28 09:31 – Updated: 2026-08-29 09:30In 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.
{
"affected": [],
"aliases": [
"CVE-2026-80668"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-28T08:16:52Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nf_conntrack_expect: use conntrack GC to reap expectations\n\nThis patch replaces the timer API by GC worker approach for\nexpectations, as it already happened in many other subsystems.\n\nUse the existing conntrack GC worker to iterate over the local list of\nexpectations in the master conntrack to reap expired expectations.\nCheck IPS_HELPER_BIT to run GC for expectations, set it on for nft_ct\nexpectation which nevers sets it. Hold the expectation spinlock while\niterating over the master conntrack expectation list to synchronize with\nnf_ct_remove_expectations(). This also performs runtime packet path\ngarbage collection through the expectation insertion and lookup\nfunctions while walking over one of the chains of the global expectation\nhashtables. Unconfirmed conntrack entries are skipped since ct-\u003eext can\nbe reallocated and dying are skipped since those will be gone soon.\nSet on IPS_HELPER_BIT if the helper ct extension is added, then the new\nGC worker does not need to bump the ct refcount to check if the ct-\u003eext\nhelper is available.\n\nThis removes the extra bump on the refcount for expectation timers, this\nallows to remove several nf_ct_expect_put() calls after the unlink,\nafter this update only refcount remains at 1 while on the expectation\nhashes.\n\nThis patch implicitly addresses a race with the existing timer API\nallowing an expectation to access a stale exp-\u003emaster pointer which has\nbeen already released when expectation removal loses races with an\nexpiring timer, ie. timer_del() reporting false.\n\nAdd a new NF_CT_EXPECT_DEAD flag to reap this expectation via GC. This\nis needed by nf_conntrack_unexpect_related() which is called in error\npaths to invalidate newly created expectations that has been added into\nthe hashes. These expectactions cannot be inmediately released as GC or\nnf_ct_remove_expectations() could race to make it. On expectation\ninsert, the runtime GC reaps stale expectations before checking the\nexpectation limit set by policy.\n\nSet current timestamp in nf_ct_expect_alloc(), then add the expectation\npolicy timeout (or custom timeout specified added on top of this) to\nspecify the expectation lifetime.",
"id": "GHSA-fpgw-998r-pg47",
"modified": "2026-08-29T09:30:27Z",
"published": "2026-08-28T09:31:48Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80668"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7ec786f4230c2a9b2eaf97a2d45368933b49d2b2"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b8b09dc2bf35a00d4e0556b5d6308c7b917ebda2"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.