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CVE Record

CVE-2026-31403: NFSD: Hold net reference for the lifetime of /proc/fs/nfs/exports fd

In the Linux kernel, the following vulnerability has been resolved: NFSD: Hold net reference for the lifetime of /proc/fs/nfs/exports fd The /proc/fs/nfs/exports proc entry is created at module init and persists for the module's lifetime. exports_proc_open() captures the caller's current network namespace and stores its svc_export_cache in seq->private, but takes no reference on the namespace. If the namespace is subsequently torn down (e.g. container destruction after the opener does setns() to a different namespace), nfsd_net_exit() calls nfsd_export_shutdown() which frees the cache. Subsequent reads on the still-open fd dereference the freed cache_detail, walking a freed hash table. Hold a reference on the struct net for the lifetime of the open file descriptor. This prevents nfsd_net_exit() from running -- and thus prevents nfsd_export_shutdown() from freeing the cache -- while any exports fd is open. cache_detail already stores its net pointer (cd->net, set by cache_create_net()), so exports_release() can retrieve it without additional per-file storage.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A local user or container may trigger a Linux kernel use-after-free involving NFSD export data and network-namespace destruction. Successful exploitation could crash the host or potentially affect kernel confidentiality and integrity. Exposure depends on NFSD, namespace use, and access to the exports proc file.

Executive priority

Prioritize NFSD servers and container hosts accessible to untrusted or lower-privileged users. The vulnerability is locally reachable rather than network-direct, but kernel-level confidentiality, integrity, and availability impacts justify prompt patching. Request vendor confirmation where appliance or distribution version mapping is unclear.

Technical view

An open /proc/fs/nfs/exports descriptor retains a pointer to a network namespace's svc_export_cache without retaining the namespace. Namespace teardown can free that cache, and later descriptor reads dereference freed memory. The fix holds a struct net reference for the descriptor's lifetime and releases it when the file closes.

Likely exposure

Linux systems running affected builds are most relevant where NFSD and network namespaces or containers are used. The supplied version data does not provide reliable distribution-specific fixed boundaries. Hosts without NFSD enabled are less likely to expose the vulnerable path, but applicability should be confirmed with the kernel distributor.

Exploitation context

The CVSS vector indicates local access, low privileges, low complexity, and no user interaction. Triggering the flaw requires an open exports descriptor combined with teardown of its network namespace. The supplied bundle marks KEV false and provides no evidence of active exploitation or public weaponization.

Researcher notes

The vulnerable lifetime relationship is between seq->private, svc_export_cache, and struct net. nfsd_net_exit() can free the cache while an exports descriptor remains open. The correction pins the namespace until exports_release(). Exact affected and fixed branch boundaries cannot be established confidently from the supplied version list alone.

Mitigation direction

  • Install a vendor-supported kernel containing the applicable upstream stable fix.
  • Confirm the running kernel after updating; installation alone may not activate the corrected kernel.
  • Until patched, restrict untrusted local or container access on hosts providing NFSD.
  • Disable unnecessary NFSD services where operationally safe.
  • Consult the referenced Siemens advisories for affected Siemens product guidance.

Validation and detection

  • Inventory running kernel builds and map them against distribution or appliance advisories.
  • Verify the applicable stable fix appears in the kernel package changelog or source.
  • Identify hosts where NFSD is enabled and network namespaces or containers are used.
  • Review access controls for /proc/fs/nfs/exports on relevant hosts.
  • Use an isolated test system to check namespace teardown for kernel memory-safety warnings.
Prepared
Confidence
medium
Sources
11

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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description · low confidence lookup

Container behavior lookup

The affected technology mentions containers, so container-specific ATT&CK technique review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-31403 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
1ADP providers
10Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2026-31403Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux96d851c4d28de8cc83fe2bd5c6bc2eb8f253a6c5, 96d851c4d28de8cc83fe2bd5c6bc2eb8f253a6c5, 96d851c4d28de8cc83fe2bd5c6bc2eb8f253a6c5, 96d851c4d28de8cc83fe2bd5c6bc2eb8f253a6c5, 96d851c4d28de8cc83fe2bd5c6bc2eb8f253a6c5, 96d851c4d28de8cc83fe2bd5c6bc2eb8f253a6c5, 96d851c4d28de8cc83fe2bd5c6bc2eb8f253a6c5unaffected
LinuxLinux3.9, 0, 5.10.253, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10, 7.0affected
Weakness

CWE details

No CWE listed

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