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CVE Record

CVE-2026-23220: ksmbd: fix infinite loop caused by next_smb2_rcv_hdr_off reset in error paths

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix infinite loop caused by next_smb2_rcv_hdr_off reset in error paths The problem occurs when a signed request fails smb2 signature verification check. In __process_request(), if check_sign_req() returns an error, set_smb2_rsp_status(work, STATUS_ACCESS_DENIED) is called. set_smb2_rsp_status() set work->next_smb2_rcv_hdr_off as zero. By resetting next_smb2_rcv_hdr_off to zero, the pointer to the next command in the chain is lost. Consequently, is_chained_smb2_message() continues to point to the same request header instead of advancing. If the header's NextCommand field is non-zero, the function returns true, causing __handle_ksmbd_work() to repeatedly process the same failed request in an infinite loop. This results in the kernel log being flooded with "bad smb2 signature" messages and high CPU usage. This patch fixes the issue by changing the return value from SERVER_HANDLER_CONTINUE to SERVER_HANDLER_ABORT. This ensures that the processing loop terminates immediately rather than attempting to continue from an invalidated offset.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2026-23220 is a Linux kernel ksmbd availability flaw. A malformed failure path during SMB2 signature checking can trap request handling in a loop, causing repeated kernel log messages and high CPU use. The source describes a kernel patch, but provides no CVSS score and no evidence of known active exploitation.

Executive priority

Treat this as a service-availability risk for SMB-serving Linux assets, especially file-sharing or appliance environments. Prioritize patch validation on externally reachable, business-critical, or operational technology systems, but do not classify it as emergency exploitation without additional evidence.

Technical view

In ksmbd, a signed request that fails SMB2 signature verification can reset next_smb2_rcv_hdr_off to zero. If the SMB2 NextCommand field remains non-zero, chained-message handling can repeatedly process the same failed request. The fix changes handling from continue to abort so the loop terminates.

Likely exposure

Exposure is most relevant to Linux systems using the in-kernel ksmbd SMB server on affected kernel lines. Systems not running ksmbd are unlikely to be exposed through this bug. Vendor kernels may backport fixes, so version checks alone may be insufficient.

Exploitation context

The CVE record does not report active exploitation, and KEV status is false. The described impact is denial of service through CPU consumption and kernel log flooding after a signed SMB2 request fails signature verification in a chained-message path.

Researcher notes

The source bundle attributes the bug to ksmbd error handling after check_sign_req failure. Affected-version data is incomplete and commit-oriented, so researchers should rely on kernel stable commits and vendor backport notes rather than raw upstream version labels alone.

Mitigation direction

  • Apply the relevant Linux stable kernel fix or vendor backport.
  • Check distribution and appliance vendor advisories for corrected kernel builds.
  • Limit network reachability to SMB services where business requirements allow.
  • Disable ksmbd where the in-kernel SMB server is not required.
  • Review the Siemens advisory if Siemens products are in scope.

Validation and detection

  • Inventory systems running Linux ksmbd or products embedding it.
  • Map deployed kernels to vendor-fixed builds or listed stable commits.
  • Check logs for repeated "bad smb2 signature" messages.
  • Review CPU spikes on SMB-serving hosts around suspicious SMB activity.
  • Confirm post-maintenance kernels include the applicable fix or backport.
Prepared
Confidence
medium
Sources
10

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-2026-23220 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
3Timeline events
1ADP providers
9Source links

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

siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux4b9b7ea1ffb1e34f01fa5726d0c184931b9ba565, 943cebf9ea3415ddefcd670d24d8883e97ba3d60, be0f89d4419dc5413a1cf06db3671c9949be0d52, be0f89d4419dc5413a1cf06db3671c9949be0d52, be0f89d4419dc5413a1cf06db3671c9949be0d52, be0f89d4419dc5413a1cf06db3671c9949be0d52, be0f89d4419dc5413a1cf06db3671c9949be0d52, 5.15.145, 6.1.71unaffected
LinuxLinux6.6, 0, 5.15.203, 6.1.164, 6.6.125, 6.12.72, 6.18.11, 6.19.1, 7.0affected
Weakness

CWE details

No CWE listed

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