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CVE Record

CVE-2026-43185: ksmbd: fix signededness bug in smb_direct_prepare_negotiation()

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix signededness bug in smb_direct_prepare_negotiation() smb_direct_prepare_negotiation() casts an unsigned __u32 value from sp->max_recv_size and req->preferred_send_size to a signed int before computing min_t(int, ...). A maliciously provided preferred_send_size of 0x80000000 will return as smaller than max_recv_size, and then be used to set the maximum allowed alowed receive size for the next message. By sending a second message with a large value (>1420 bytes) the attacker can then achieve a heap buffer overflow. This fix replaces min_t(int, ...) with min_t(u32)

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A flaw in Linux’s ksmbd file-sharing server allows an unauthenticated remote attacker to corrupt kernel heap memory during SMB Direct negotiation. Successful exploitation could severely affect data confidentiality, integrity, and system availability. Actual exposure depends on ksmbd use, kernel patch status, and network reachability.

Executive priority

Treat remediation as urgent for internet-facing or otherwise untrusted-reachable ksmbd systems. Quickly establish whether ksmbd and SMB Direct are present before assigning fleet-wide emergency priority. Patch confirmed exposure promptly because exploitation requires no credentials or user action and may compromise all three security objectives.

Technical view

An unsigned 32-bit negotiation size is incorrectly compared as a signed integer in smb_direct_prepare_negotiation(). An attacker-controlled value can therefore establish an unsafe receive-size limit, allowing a subsequent message to cause a heap buffer overflow. The fix performs the comparison using u32 values.

Likely exposure

Linux hosts are most likely exposed when they run an affected kernel, use ksmbd, and permit untrusted access to SMB Direct negotiation. The supplied version entries are insufficiently clear for reliable distribution-level mapping, so confirm each kernel’s backport status with its distributor.

Exploitation context

The supplied CVSS 3.1 score is 9.8: network-accessible, low complexity, requiring neither privileges nor user interaction. The bundle marks KEV false and provides no evidence of active exploitation or a public exploit. Treat this as a high-risk reachable vulnerability, not a confirmed exploited one.

Researcher notes

The record identifies a signedness error corrected by replacing min_t(int, ...) with min_t(u32, ...). No CWE is supplied. The affected-version entries contain duplication and unclear boundaries, so precise distribution and backport claims require vendor confirmation. The cited commits are the strongest supplied references for fix verification.

Mitigation direction

  • Update to a distribution kernel incorporating the referenced fix; verify backport status with the Linux distributor.
  • Prioritize hosts where ksmbd is enabled and SMB Direct negotiation is reachable from untrusted networks.
  • If updating is delayed, request vendor-approved temporary mitigations; none are specified in the supplied sources.

Validation and detection

  • Inventory Linux kernel builds and identify hosts using ksmbd.
  • Determine whether SMB Direct negotiation is reachable from untrusted network segments.
  • Map each distribution kernel to vendor guidance or the three referenced stable commits.
  • After updating, confirm the running kernel includes the unsigned u32 comparison correction.
  • Document systems whose affected status cannot be confidently resolved from the supplied version data.
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-2026-43185 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
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
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-2026-43185Attack 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
LinuxLinux0626e6641f6b467447c81dd7678a69c66f7746cf, 0626e6641f6b467447c81dd7678a69c66f7746cf, 0626e6641f6b467447c81dd7678a69c66f7746cfunaffected
LinuxLinux5.15, 0, 6.18.16, 6.19.6, 7.0affected
Weakness

CWE details

No CWE listed

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