Bug 2514444 (CVE-2026-68431)

Summary: CVE-2026-68431 kernel: ksmbd: validate minimum PDU size for transform requests
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in ksmbd in the Linux kernel. When handling Server Message Block version 2 (SMB2) transform requests, the system fails to validate the minimum Protocol Data Unit (PDU) size. An unauthenticated remote attacker can send a specially crafted, short transform packet, bypassing security checks. This leads to the system reading beyond allocated memory and potentially disclosing sensitive information to the attacker.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-12 00:21:44 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: validate minimum PDU size for transform requests

The receive path applies the minimum SMB2 PDU size check only when
ProtocolId is SMB2_PROTO_NUMBER. A packet carrying
SMB2_TRANSFORM_PROTO_NUM bypasses the check even when the negotiated
dialect does not provide transform handling.

On an SMB 2.1 connection, a short transform packet therefore reaches
init_smb2_rsp_hdr(), which interprets the request as a full SMB2 header
and reads beyond the request allocation. The copied fields can then be
returned to the unauthenticated client.

Compression transforms are converted to ordinary SMB2 messages before
protocol validation. After that conversion, validate ordinary SMB2
requests against SMB2_MIN_SUPPORTED_PDU_SIZE and require encryption
transform requests to contain both a transform header and an SMB2
header. This rejects truncated requests before work allocation.
Comment 1 Mauro Matteo Cascella 2026-08-12 15:35:22 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081254-CVE-2026-68431-12d7@gregkh/T