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Full vulnerability report · 2024
CVE-2021-47316High confidence

nfsd: fix NULL dereference in nfs3svc_encode_getaclres

Linux · Linux

7.5HighCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 91 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:High, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 0.62% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Linux Linux and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 30 daysRemediation target: Within 180 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 91 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

4 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcelinuxNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcelinuxNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcelinuxNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcelinuxNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

3 current
CVE-2021-47316 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitykernel: nfsd: fix NULL dereference in nfs3svc_encode_getaclres
90 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • kernel as a component of Red Hat Enterprise Linux 6
  • kernel-abi-whitelists as a component of Red Hat Enterprise Linux 6
  • kernel-bootwrapper as a component of Red Hat Enterprise Linux 6
  • kernel-debug as a component of Red Hat Enterprise Linux 6
  • kernel-debug-devel as a component of Red Hat Enterprise Linux 6
  • kernel-devel as a component of Red Hat Enterprise Linux 6
  • kernel-doc as a component of Red Hat Enterprise Linux 6
  • kernel-firmware as a component of Red Hat Enterprise Linux 6
  • kernel-headers as a component of Red Hat Enterprise Linux 6
  • kernel-kdump as a component of Red Hat Enterprise Linux 6
  • kernel-kdump-devel as a component of Red Hat Enterprise Linux 6
  • kernel.src as a component of Red Hat Enterprise Linux 6
Summary
A vulnerability was found in the nfs3svc_encode_getaclres function in the Linux kernel's NFS server, where the function may encounter a NULL pointer for a directory entry (dentry), which can lead to a system crash or instability when accessed improperly.
Remediation
Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.
SSA-265688 · CSAF 2.0 · revision 13 · interimSiemens ProductCERTSSA-265688: Vulnerabilities in the additional GNU/Linux subsystem of the SIMATIC S7-1500 TM MFP V1.1
1 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
Summary
nfsd: NULL dereference in nfs3svc_encode_getaclres.
Remediation
Limit access to the interactive shell of the additional GNU/Linux subssytem to trusted personnel only.
SSA-355557 · CSAF 2.0 · revision 3 · interimSiemens ProductCERTSSA-355557: Multiple Vulnerabilities in Third-Party Components in SINEC OS before V3.2
3 known not affected

The vendor explicitly states that these products are not affected by this CVE.

  • RUGGEDCOM RST2428P (6GK6242-6PA00)
  • SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 family
  • SCALANCE XCM-/XRM-/XCH-/XRH-300 family
Summary
nfsd: NULL dereference in nfs3svc_encode_getaclres.
Remediation
No remediation text is recorded.
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-34321

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 91 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix NULL dereference in nfs3svc_encode_getaclres In error cases the dentry may be NULL. Before 20798dfe249a, the encoder also checked dentry and d_really_is_positive(dentry), but that looks like overkill to me--zero status should be enough to guarantee a positive dentry. This isn't the first time we've seen an error-case NULL dereference hidden in the initialization of a local variable in an xdr encoder. But I went back through the other recent rewrites and didn't spot any similar bugs.

What

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix NULL dereference in nfs3svc_encode_getaclres In error cases the dentry may be NULL. Before 20798dfe249a, the encoder also checked dentry and d_really_is_positive(dentry), but that looks like overkill to me--zero status should be enough to guarantee a positive dentry. This isn't the first time we've seen an error-case NULL dereference hidden in the initialization of a local variable in an xdr encoder. But I went back through the other recent rewrites and didn't spot any similar bugs.

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix NULL dereference in nfs3svc_encode_getaclres In error cases the dentry may be NULL. Before 20798dfe249a, the encoder also checked dentry and d_really_is_positive(dentry), but that looks like overkill to me--zero status should be enough to guarantee a positive dentry. This isn't the first time we've seen an error-case NULL dereference hidden in the initialization of a local variable in an xdr encoder. But I went back through the other recent rewrites and didn't spot any similar bugs.

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → NULL Pointer Dereference → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-476 ↗

CWE-476: NULL Pointer Dereference. The product dereferences a pointer that it expects to be valid but is NULL.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-476
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

Cyber Security Agency of Singapore · English · CSA-SB-20240522Security Bulletin 22 May 2024

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 22 May 2024, published on 22 May 2024. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2025-AVI-1057Multiples vulnérabilités dans les produits VMware

d?id=CVE-2021-47223 Référence CVE CVE-2021-47226 https://www.cve.org/CVERecord?id=CVE-2021-47226 Référence CVE CVE-2021-47227 https://www.cve.org/CVERecord?id=CVE-2021-47227 Référence CVE CVE-2021-47237 https://www.cve.org/CVERecord?id=CVE-2021-47237 Référence CVE CVE-2021-47239 https://www.cve.org/CVERecord?id=CVE-2021-47239 Référence CVE CVE-2021-47250 https://www.cve.org/CVERecord?id=CVE-2021-47250 Référence CVE CVE-2021-47251 https://www.cve.org/CVERecord?id=CVE-2021-47251 Référence CVE CVE-2021-47261 https://www.cve.org/CVERecord?id=CVE-2021-47261 Référence CVE CVE-2021-47266 https://www.cve.org/CVERecord?id=CVE-2021-47266 Référence CVE CVE-2021-47316 https://www.cve.org/CVERecord?id=CVE-2021-47316 Référence CVE CVE-2021-47318 https://www.cve.org/CVERecord?id=CVE-2021-47318 Référence CVE CVE-2021-47325 https://www.cve.org/CVERecord?id=CVE-2021-47325 Référence CVE CVE-2021-47343 https://www.cve.org/CVERecord?id=CVE-2021-47343 Référence CVE CVE-2021-47346 https://www.cve.org/CVERecord?id=CVE-2021-47346 Référence CVE CVE-2021-47349 https://www.cve.org/CVERecord?id=CVE-2021-47349 Référence CVE CVE-2021-47360 https://www.cve.org/CVERecord?id=CVE-2021-47360 Référence CVE CVE-2021-47365 https://www.cve.org/CVERecord?id=CVE-2021-47365 Référence CVE CVE-2021-47373 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2025-AVI-0677Multiples vulnérabilités dans les produits Siemens

août 2025 https://cert-portal.siemens.com/productcert/html/ssa-529291.html Bulletin de sécurité Siemens SSA-613116 du 12 août 2025 https://cert-portal.siemens.com/productcert/html/ssa-613116.html Bulletin de sécurité Siemens SSA-693808 du 12 août 2025 https://cert-portal.siemens.com/productcert/html/ssa-693808.html Bulletin de sécurité Siemens SSA-707630 du 12 août 2025 https://cert-portal.siemens.com/productcert/html/ssa-707630.html Bulletin de sécurité Siemens SSA-894058 du 12 août 2025 https://cert-portal.siemens.com/productcert/html/ssa-894058.html Référence CVE CVE-2021-44879 https://www.cve.org/CVERecord?id=CVE-2021-44879 Référence CVE CVE-2021-47316 https://www.cve.org/CVERecord?id=CVE-2021-47316 Référence CVE CVE-2022-48666 https://www.cve.org/CVERecord?id=CVE-2022-48666 Référence CVE CVE-2022-48827 https://www.cve.org/CVERecord?id=CVE-2022-48827 Référence CVE CVE-2022-48828 https://www.cve.org/CVERecord?id=CVE-2022-48828 Référence CVE CVE-2022-48829 https://www.cve.org/CVERecord?id=CVE-2022-48829 Référence CVE CVE-2022-48935 https://www.cve.org/CVERecord?id=CVE-2022-48935 Référence CVE CVE-2022-49034 https://www.cve.org/CVERecord?id=CVE-2022-49034 Référence CVE CVE-2023-3567 https://www.cve.org/CVERecord?id=CVE-2023-3567 Référence CVE CVE-2023-35827 https://www.cve.org/CVERecord?id=CV

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-021426Linux の Linux Kernel における NULL ポインタデリファレンスに関する脆弱性

Linux の Linux Kernel には、NULL ポインタデリファレンスに関する脆弱性が存在します。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix availability varies by product
Affected
Fixed
Linux: < 5.13, 5.13.4 ≤ 5.13.*, 5.14 ≤ *
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.
04

Evidence and provenance

Published 21 May 2024 · Last source change 5 Aug 2026, 08:47 UTC · CWE-476 · NULL Pointer Dereference

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-34321
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceNIST NVD
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-34321↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Patch or update reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-47316 · cve.blacktree.nl