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CVE-2024-50121: nfsd: cancel nfsd_shrinker_work using sync mode in nfs4_state_shutdown_net

In the Linux kernel, the following vulnerability has been resolved: nfsd: cancel nfsd_shrinker_work using sync mode in nfs4_state_shutdown_net In the normal case, when we excute `echo 0 > /proc/fs/nfsd/threads`, the function `nfs4_state_destroy_net` in `nfs4_state_shutdown_net` will release all resources related to the hashed `nfs4_client`. If the `nfsd_client_shrinker` is running concurrently, the `expire_client` function will first unhash this client and then destroy it. This can lead to the following warning. Additionally, numerous use-after-free errors may occur as well. nfsd_client_shrinker echo 0 > /proc/fs/nfsd/threads expire_client nfsd_shutdown_net unhash_client ... nfs4_state_shutdown_net /* won't wait shrinker exit */ /* cancel_work(&nn->nfsd_shrinker_work) * nfsd_file for this /* won't destroy unhashed client1 */ * client1 still alive nfs4_state_destroy_net */ nfsd_file_cache_shutdown /* trigger warning */ kmem_cache_destroy(nfsd_file_slab) kmem_cache_destroy(nfsd_file_mark_slab) /* release nfsd_file and mark */ __destroy_client ==================================================================== BUG nfsd_file (Not tainted): Objects remaining in nfsd_file on __kmem_cache_shutdown() -------------------------------------------------------------------- CPU: 4 UID: 0 PID: 764 Comm: sh Not tainted 6.12.0-rc3+ #1 dump_stack_lvl+0x53/0x70 slab_err+0xb0/0xf0 __kmem_cache_shutdown+0x15c/0x310 kmem_cache_destroy+0x66/0x160 nfsd_file_cache_shutdown+0xac/0x210 [nfsd] nfsd_destroy_serv+0x251/0x2a0 [nfsd] nfsd_svc+0x125/0x1e0 [nfsd] write_threads+0x16a/0x2a0 [nfsd] nfsctl_transaction_write+0x74/0xa0 [nfsd] vfs_write+0x1a5/0x6d0 ksys_write+0xc1/0x160 do_syscall_64+0x5f/0x170 entry_SYSCALL_64_after_hwframe+0x76/0x7e ==================================================================== BUG nfsd_file_mark (Tainted: G B W ): Objects remaining nfsd_file_mark on __kmem_cache_shutdown() -------------------------------------------------------------------- dump_stack_lvl+0x53/0x70 slab_err+0xb0/0xf0 __kmem_cache_shutdown+0x15c/0x310 kmem_cache_destroy+0x66/0x160 nfsd_file_cache_shutdown+0xc8/0x210 [nfsd] nfsd_destroy_serv+0x251/0x2a0 [nfsd] nfsd_svc+0x125/0x1e0 [nfsd] write_threads+0x16a/0x2a0 [nfsd] nfsctl_transaction_write+0x74/0xa0 [nfsd] vfs_write+0x1a5/0x6d0 ksys_write+0xc1/0x160 do_syscall_64+0x5f/0x170 entry_SYSCALL_64_after_hwframe+0x76/0x7e To resolve this issue, cancel `nfsd_shrinker_work` using synchronous mode in nfs4_state_shutdown_net.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2024-50121 is a Linux kernel NFS server bug where shutdown can race with background cleanup and leave freed client-related objects in use. The reported impact is high because use-after-free in kernel code can affect confidentiality, integrity, and availability, but the source bundle does not show active exploitation.

Executive priority

Treat as a high-priority kernel maintenance item for NFS-serving systems, especially shared infrastructure and appliances. The business risk is mainly local privilege-adjacent kernel compromise or service disruption, not confirmed internet-scale exploitation from the provided evidence.

Technical view

The flaw is in nfsd shutdown handling. nfs4_state_shutdown_net cancelled nfsd_shrinker_work without waiting, allowing nfsd_client_shrinker to concurrently unhash and later destroy an nfs4_client. The fix changes cancellation to synchronous mode so cleanup completes before state and file cache teardown.

Likely exposure

Exposure is most relevant to Linux systems running the in-kernel NFS server on affected kernel branches or downstream products. The CVSS vector is local, low-complexity, low-privilege, no user interaction. Confirm exact exposure through kernel version, distro backports, and vendor advisories.

Exploitation context

The bundle marks KEV as false and provides no cited evidence of exploitation in the wild. The described trigger involves local interaction with nfsd shutdown behavior and a race with shrinker cleanup. Do not treat this as remotely exploitable from the supplied evidence.

Researcher notes

The core bug is a race between nfsd_client_shrinker and nfs4_state_shutdown_net during nfsd teardown, producing use-after-free conditions and slab shutdown warnings. The supplied fix direction is synchronous cancellation of nfsd_shrinker_work. Affected-version metadata is incomplete without distro backport interpretation.

Mitigation direction

  • Apply vendor kernel updates containing the referenced Linux stable fixes.
  • Prioritize NFS server hosts and appliances that enable nfsd.
  • Review Debian LTS and Siemens advisories for downstream package guidance.
  • If no update is available, follow vendor guidance for temporary risk reduction.
  • Retire or isolate unused NFS server functionality where operationally acceptable.

Validation and detection

  • Inventory Linux systems and products that run the in-kernel NFS server.
  • Map installed kernels to vendor-fixed packages or referenced stable commits.
  • Check Debian LTS applicability for Debian-based affected environments.
  • Review Siemens advisory applicability for listed industrial products.
  • Confirm vulnerability scanners account for distro backports, not version strings alone.
Prepared
Confidence
high
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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cwe · low confidence lookup

CWE-416: Exact CWE lookup

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cve · low confidence lookup

CVE-2024-50121 mapping review

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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
3ADP providers
10Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

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:H1.85.9CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2024-50121Attack 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

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux2bbf10861d51dae76c6da7113516d0071c782653, 958294a3eb82026fcfff20b0287a90e9c854785e, f3ea5ec83d1a827f074b2b660749817e0bf2b23e, 7c24fa225081f31bc6da6a355c1ba801889ab29a, 7c24fa225081f31bc6da6a355c1ba801889ab29a, 7c24fa225081f31bc6da6a355c1ba801889ab29aunaffected
LinuxLinux6.2, 0, 5.10.233, 5.15.176, 6.1.123, 6.6.59, 6.11.6, 6.12affected
Weakness

CWE details

CWE-416

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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