CVE-2026-68431 ksmbd: validate minimum PDU size for transform requests
An unauthenticated attacker can read memory beyond the request allocation by sending a short SMB2 transform packet to the ksmbd kernel module.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68431?
CVE-2026-68431 is a critical vulnerability in Linux, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-68431?
How do I fix CVE-2026-68431?
Apply the vendor's patch.
Is CVE-2026-68431 being exploited?
There is no known exploitation of CVE-2026-68431 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-68431, DEBIAN-CVE-2026-68431, GHSA-6pm5-g7cv-g948, UBUNTU-CVE-2026-68431.