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CVE Record

CVE-2026-46029: mm/slab: return NULL early from kmalloc_nolock() in NMI on UP

In the Linux kernel, the following vulnerability has been resolved: mm/slab: return NULL early from kmalloc_nolock() in NMI on UP On UP kernels (!CONFIG_SMP), spin_trylock() is a no-op that unconditionally succeeds even when the lock is already held. As a result, kmalloc_nolock() called from NMI context can re-enter the slab allocator and acquire n->list_lock that the interrupted context is already holding, corrupting slab state. With CONFIG_DEBUG_SPINLOCK on UP, the following BUG is triggered with the slub_kunit test module: BUG: spinlock trylock failure on UP on CPU#0, kunit_try_catch/243 [...] Call Trace: <NMI> dump_stack_lvl+0x3f/0x60 do_raw_spin_trylock+0x41/0x50 _raw_spin_trylock+0x24/0x50 get_from_partial_node+0x120/0x4d0 ___slab_alloc+0x8a/0x4c0 kmalloc_nolock_noprof+0x164/0x310 [...] </NMI> Fix this by returning NULL early when invoked from NMI on a UP kernel.

HighCVSS 7Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel slab allocator flaw can corrupt memory when a single-processor kernel performs a specific allocation during a non-maskable interrupt. Successful abuse requires local access and difficult timing, but potential confidentiality, integrity, and availability impacts are high. The issue is narrowly configuration-dependent.

Executive priority

Prioritize prompt assessment rather than an emergency fleet-wide response. Identify uniprocessor kernels first, especially systems permitting untrusted local code. Patch confirmed exposure through supported vendor channels. Lower priority is reasonable for SMP-enabled builds once configuration and package status are verified.

Technical view

On !CONFIG_SMP kernels, spin_trylock() always succeeds, allowing kmalloc_nolock() in NMI context to re-enter an already-locked slab allocator and corrupt slab state. The upstream fix returns NULL before allocation in this condition. The supplied CVSS v3.1 score is 7.0: local, high-complexity, low-privilege exploitation without user interaction.

Likely exposure

Exposure is limited to affected Linux releases running uniprocessor builds without CONFIG_SMP, where kmalloc_nolock() can execute from NMI context. The bundle lists 6.18, 6.18.27, 7.0.4, and 7.1 as affected, but also contains an ambiguous "0" entry; confirm exact vendor package status.

Exploitation context

The bundle provides no evidence of active exploitation, and the CVE is not listed as KEV. The CVSS vector indicates local access, low privileges, and high attack complexity. A KUnit test with debug spinlocks demonstrated the faulty lock behavior; that is evidence of the bug, not confirmed malicious exploitation.

Researcher notes

The defect is a UP-only re-entrancy failure in slab allocation during NMI. CONFIG_DEBUG_SPINLOCK and slub_kunit expose a trylock failure. The record supplies three stable-kernel commits but does not map each commit to every affected version in the bundle. No CWE, public exploit, or exploitation campaign is identified.

Mitigation direction

  • Update to a vendor-supported kernel release that incorporates the referenced stable fix.
  • If updating is delayed, ask the vendor for a validated backport or configuration-specific mitigation.
  • Prioritize affected uniprocessor systems handling untrusted local workloads.
  • Test operational behavior because the fix makes the affected allocation return NULL in NMI context.

Validation and detection

  • Record kernel package versions and map them to vendor CVE advisories or fixed builds.
  • Check whether each kernel was built without CONFIG_SMP.
  • Confirm the installed kernel contains the applicable referenced stable commit.
  • Exercise representative workloads in staging and check for allocator failures or kernel instability.
Prepared
Confidence
medium
Sources
5

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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CVE-2026-46029 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:H/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
0ADP providers
4Source 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
7CVSS 3.1HighCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H15.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7High
CVSS 3.1 vector shape for CVE-2026-46029Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:H/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.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxaf92793e52c3a99b828ed4bdd277fd3e11c18d08, af92793e52c3a99b828ed4bdd277fd3e11c18d08, af92793e52c3a99b828ed4bdd277fd3e11c18d08unaffected
LinuxLinux6.18, 0, 6.18.27, 7.0.4, 7.1affected
Weakness

CWE details

No CWE listed

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