Linux Kernel: Use-After-Free (CVE-2026-89688)
Published Last modified Sources: SUSE, Debian, Debian LTS, CVE.org, BSI
What is affected, what to do
In the Linux kernel, the following vulnerability has been resolved: nfsd: drop the stateid, not the stateowner, on seqid_op replay retry In nfs4_preprocess_seqid_op() the stateid is obtained from nfsd4_lookup_stateid(), which holds a reference on the nfs4_stid (sc_count) but takes no reference on the stateowner. openlockstateid() merely casts that stid and likewise takes no reference. When nfsd4_cstate_assign_replay() returns -EAGAIN (the replay owner is being torn down, RP_UNHASHED) it has not taken a stateowner reference on that path.
Update Linux Kernel to version 6.12.109, Linux Kernel to version 6.18.50, Linux Kernel to version 7.2.4.
- Affected
- Linux Kernel
lt 6.10..6.12.109 - Linux Kernel
lt 6.13..6.18.50 - Linux Kernel
lt 6.19..7.2.4
- Linux Kernel
- Fixed in
- Linux Kernel
6.12.109 - Linux Kernel
6.18.50 - Linux Kernel
7.2.4 - Linux Kernel
7.3
- Linux Kernel
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Metrics
9.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
9.8
CVSS v3
Severity Critical on the scale from 0 to 10.
Source: SUSE, Debian, Debian LTS, CVE.org, BSI
0.7 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 54.2
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 99.39 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 9.8 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 9.8
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.7 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 54.2
- High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
In the Linux kernel, the following vulnerability has been resolved: nfsd: drop the stateid, not the stateowner, on seqid_op replay retry In nfs4_preprocess_seqid_op() the stateid is obtained from nfsd4_lookup_stateid(), which holds a reference on the nfs4_stid (sc_count) but takes no reference on the stateowner. openlockstateid() merely casts that stid and likewise takes no reference. When nfsd4_cstate_assign_replay() returns -EAGAIN (the replay owner is being torn down, RP_UNHASHED) it has not taken a stateowner reference on that path. The error handling nevertheless called nfs4_put_stateowner(stp->st_stateowner), dropping an so_count reference the function never acquired -- risking a stateowner refcount underflow and use-after-free -- while leaking the sc_count reference held on the stid. The leaked stid reference can also stall a concurrent nfsd4_close_open_stateid() waiting for sc_count to drop. Drop the reference actually held -- the stid -- before retrying. The stateowner stays alive through the reference held by the stid. This mirrors the open path in nfsd4_process_open1(), where the put balances a reference that path explicitly holds on the stateowner.
Source: suse_csaf, Debian Security Advisories, Debian LTS Advisories, cvelistv5, NVD (NIST), BSI WID Portal, BSI CSAF
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| Linux | Linux |
|
|
Vendors and products
Affected operating systems
| Linux | debian | linux | trixie |
| Linux | debian | linux-6.12 | bookworm |
References & sources
- git.kernel.orgstable/c/69ed78b6b947c9257213164678b4edf17533093b
- git.kernel.orgstable/c/00843074d9b84824552c9679d423d29500ca5de0
- git.kernel.orgstable/c/f7cb90ddc021747fc9abfd4cf5252d425fd34eec
- git.kernel.orgstable/c/5e4627d3513e60accfce9d5f4c7fa95251ef93d6
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedLinux
1 individual change: Affected versions (publisher)
Show the original change
Individual changes of this event as published by NVD Type Action Before After Affected versions (publisher) added —Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/89xxx/CVE-2026-89688.json">CVE-2026-89688</a>Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Record modifiedLinux
CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Show the original change
Individual changes of this event as published by NVD Type Action Before After CVSS added —AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSource identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
ReceivedLinux
Description added or changed
New references:Show 6 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —In the Linux kernel, the following vulnerability has been resolved: nfsd: drop the stateid, not the stateowner, on seqid_op replay retry In nfs4_preprocess_seqid_op() the stateid is obtained from nfsd4_lookup_stateid(), which holds a reference on the nfs4_stid (sc_count) but takes no reference on the stateowner. openlockstateid() merely casts that stid and likewise takes no reference. When nfsd4_cstate_assign_replay() returns -EAGAIN (the replay owner is being torn down, RP_UNHASHED) it has not taken a stateowner reference on that path. The error handling nevertheless called nfs4_put_stateowner(stp->st_stateowner), dropping an so_count reference the function never acquired -- risking a stateowner refcount underflow and use-after-free -- while leaking the sc_count reference held on the stid. The leaked stid reference can also stall a concurrent nfsd4_close_open_stateid() waiting for sc_count to drop. Drop the reference actually held -- the stid -- before retrying. The stateowner stays alive through the reference held by the stid. This mirrors the open path in nfsd4_process_open1(), where the put balances a reference that path explicitly holds on the stateowner.Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/89xxx/CVE-2026-89688.json">CVE-2026-89688</a>Reference added —https://git.kernel.org/stable/c/00843074d9b84824552c9679d423d29500ca5de0Reference added —https://git.kernel.org/stable/c/5e4627d3513e60accfce9d5f4c7fa95251ef93d6Reference added —https://git.kernel.org/stable/c/69ed78b6b947c9257213164678b4edf17533093bReference added —https://git.kernel.org/stable/c/f7cb90ddc021747fc9abfd4cf5252d425fd34eecSource identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-89688"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-89688.svg?lang=en" alt="CVE-2026-89688 – NEOSEC Intel" height="20"></a>