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CVE Record

CVE-2025-38523: cifs: Fix the smbd_response slab to allow usercopy

In the Linux kernel, the following vulnerability has been resolved: cifs: Fix the smbd_response slab to allow usercopy The handling of received data in the smbdirect client code involves using copy_to_iter() to copy data from the smbd_reponse struct's packet trailer to a folioq buffer provided by netfslib that encapsulates a chunk of pagecache. If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks then performed in copy_to_iter() oopsing with something like the following: CIFS: Attempting to mount //172.31.9.1/test CIFS: VFS: RDMA transport established usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)! ------------[ cut here ]------------ kernel BUG at mm/usercopy.c:102! ... RIP: 0010:usercopy_abort+0x6c/0x80 ... Call Trace: <TASK> __check_heap_object+0xe3/0x120 __check_object_size+0x4dc/0x6d0 smbd_recv+0x77f/0xfe0 [cifs] cifs_readv_from_socket+0x276/0x8f0 [cifs] cifs_read_from_socket+0xcd/0x120 [cifs] cifs_demultiplex_thread+0x7e9/0x2d50 [cifs] kthread+0x396/0x830 ret_from_fork+0x2b8/0x3b0 ret_from_fork_asm+0x1a/0x30 The problem is that the smbd_response slab's packet field isn't marked as being permitted for usercopy. Fix this by passing parameters to kmem_slab_create() to indicate that copy_to_iter() is permitted from the packet region of the smbd_response slab objects, less the header space.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in Linux CIFS SMB Direct handling can crash an affected kernel while processing received file-share data. The documented impact is loss of availability, not data theft or modification. Exposure depends on the affected kernel code, CIFS over RDMA use, and hardened usercopy configuration.

Executive priority

Treat as a high-priority availability issue for affected file-service workloads, especially where a kernel crash would disrupt critical operations. Rapidly identify CIFS-over-RDMA systems and schedule supported kernel updates. Broader emergency action is not supported without evidence that the relevant configuration is deployed.

Technical view

The smbd_response slab did not permit usercopy from its packet region. With CONFIG_HARDENED_USERCOPY enabled, copy_to_iter() can detect the transfer as prohibited and trigger a kernel BUG during CIFS SMB Direct receive processing. The upstream resolution marks the permitted packet area when creating the slab.

Likely exposure

Likely exposure is concentrated in Linux systems using affected kernels with CIFS SMB Direct/RDMA and CONFIG_HARDENED_USERCOPY enabled. The bundle lists Linux versions including 6.12, 6.12.36, 6.15.8, and 6.16, but does not clearly define complete ranges or distribution-specific package status.

Exploitation context

The supplied CVSS rates this as network-accessible, low-complexity, unauthenticated, and availability-only. KEV is false, and the bundle provides no evidence of active exploitation or a public exploit. Practical triggering appears tied to CIFS SMB Direct receive activity.

Researcher notes

The failure is a slab usercopy-whitelisting defect rather than documented memory disclosure. The fix permits copying only from the packet region, excluding header space. The supplied version data is ambiguous and lacks distribution mappings; validate exposure against vendor packages and the three stable-kernel commits. No CWE was supplied.

Mitigation direction

  • Update to a vendor-supported kernel containing the applicable upstream stable fix.
  • Check distribution or appliance vendor advisories for corrected package versions.
  • Prioritize systems actively using CIFS SMB Direct/RDMA with hardened usercopy enabled.
  • If updates are unavailable, ask the vendor for supported temporary mitigation guidance.

Validation and detection

  • Inventory kernel versions on systems providing or consuming CIFS shares.
  • Confirm whether CONFIG_HARDENED_USERCOPY is enabled in deployed kernel configurations.
  • Identify hosts using CIFS SMB Direct or RDMA transport.
  • Verify vendor package changelogs or source trees include an applicable referenced fix commit.
  • Review kernel logs for hardened-usercopy alerts, CIFS receive failures, BUG messages, or unexpected reboots.
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-2025-38523 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2025-38523Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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
LinuxLinuxee4cdf7ba857a894ad1650d6ab77669cbbfa329e, ee4cdf7ba857a894ad1650d6ab77669cbbfa329e, ee4cdf7ba857a894ad1650d6ab77669cbbfa329eunaffected
LinuxLinux6.12, 0, 6.12.36, 6.15.8, 6.16affected
Weakness

CWE details

No CWE listed

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