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CVE Record

CVE-2026-31444: ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free and NULL deref in smb_grant_oplock() smb_grant_oplock() has two issues in the oplock publication sequence: 1) opinfo is linked into ci->m_op_list (via opinfo_add) before add_lease_global_list() is called. If add_lease_global_list() fails (kmalloc returns NULL), the error path frees the opinfo via __free_opinfo() while it is still linked in ci->m_op_list. Concurrent m_op_list readers (opinfo_get_list, or direct iteration in smb_break_all_levII_oplock) dereference the freed node. 2) opinfo->o_fp is assigned after add_lease_global_list() publishes the opinfo on the global lease list. A concurrent find_same_lease_key() can walk the lease list and dereference opinfo->o_fp->f_ci while o_fp is still NULL. Fix by restructuring the publication sequence to eliminate post-publish failure: - Set opinfo->o_fp before any list publication (fixes NULL deref). - Preallocate lease_table via alloc_lease_table() before opinfo_add() so add_lease_global_list() becomes infallible after publication. - Keep the original m_op_list publication order (opinfo_add before lease list) so concurrent opens via same_client_has_lease() and opinfo_get_list() still see the in-flight grant. - Use opinfo_put() instead of __free_opinfo() on err_out so that the RCU-deferred free path is used. This also requires splitting add_lease_global_list() to take a preallocated lease_table and changing its return type from int to void, since it can no longer fail.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A Linux kernel SMB server flaw can cause memory misuse or a crash when oplock data becomes visible to concurrent processing too early. The supplied CVSS score is 9.8, indicating potentially severe confidentiality, integrity, and availability impact. Actual risk depends on whether ksmbd is enabled, reachable, and missing the applicable stable-kernel fix.

Executive priority

Prioritize immediate exposure assessment and expedited patching for internet-facing or broadly reachable ksmbd servers. The technical impact and CVSS rating justify critical handling, while the absence of confirmed exploitation slightly reduces emergency-response urgency. Do not assume safety from version numbering alone; verify vendor backports.

Technical view

In ksmbd, smb_grant_oplock() could publish oplock state before initialization and failure handling were safe. Concurrent readers could access a freed opinfo or dereference a NULL o_fp. The fix initializes fields before publication, preallocates the lease table, removes post-publication allocation failure, and uses RCU-deferred opinfo_put() cleanup.

Likely exposure

Exposure is most plausible on systems running the Linux ksmbd SMB server with network-reachable SMB service and without the relevant stable-kernel commit. The bundle identifies fixed commits and versions marked unaffected, but does not provide complete vulnerable version ranges. Systems not using ksmbd are unlikely to reach this code path.

Exploitation context

The CVSS vector describes network access, low complexity, no privileges, and no user interaction. However, the supplied record is not in KEV and provides no evidence of exploitation in the wild or a public proof of concept. Treat exploitability as a serious potential risk, not confirmed active exploitation.

Researcher notes

The defect combines a dangling list entry after allocation failure with premature global lease publication before o_fp assignment. The remediation preserves m_op_list ordering for concurrent lease visibility while making subsequent global-list publication infallible. Complete vulnerable ranges, triggering reliability, and exploitation evidence are absent from the supplied sources.

Mitigation direction

  • Inventory systems running or loading ksmbd and identify their exact kernel builds.
  • Apply the vendor-supported kernel update containing the applicable referenced stable fix.
  • Restrict SMB access to trusted networks while updates are evaluated and deployed.
  • Check distribution or appliance vendor guidance for backported fixes and reboot requirements.

Validation and detection

  • Confirm ksmbd is disabled or the running kernel includes the applicable stable fix.
  • Compare vendor kernel changelogs against CVE-2026-31444 and the referenced commits.
  • Verify SMB exposure from relevant network zones using approved defensive asset discovery.
  • Monitor affected hosts for kernel crashes or ksmbd-related fault reports.
Prepared
Confidence
medium
Sources
7

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-2026-31444 mapping review

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/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
6Source 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
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2026-31444Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/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
LinuxLinux302fef75512b2c8329a3f5efab1ae7ba2562387a, 08aa9f3c8cf4d0bee44df540dfe34e8d64069f2c, 1d6abf145615dbfe267ce3b0a271f95e3780e18e, ce8507ee82c888126d8e7565e27c016308d24cde, 1dfd062caa165ec9d7ee0823087930f3ab8a6294unaffected
LinuxLinux6.6.130, 6.12.78, 6.18.19, 6.19.9unaffected
Weakness

CWE details

No CWE listed

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