CVE-2026-46139 smb: client: use kzalloc to zero-initialize security descriptor buffer
Uninitialized memory in the Linux kernel SMB client may leak heap data, potentially exposing sensitive information to attackers.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-46139?
CVE-2026-46139 is a medium-severity vulnerability in Linux kernel, published on 28 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
smb: client: use kzalloc to zero-initialize security descriptor buffer
Commit 62e7dd0a39c2d ("smb: common: change the data type of num_aces to le16") split struct smb_acl's __le32 num_aces field into __le16 num_aces and __le16 reserved. The reserved field corresponds to Sbz2 in the MS-DTYP ACL wire format, which must be zero [1].
When building an ACL descriptor in build_sec_desc(), we are using a kmalloc()'ed descriptor buffer and writing the fields explicitly using le16() writes now. This never writes to the 2 byte reserved field, leaving it as uninitialized heap data.
When the reserved field happens to contain non-zero slab garbage, Samba rejects the security descriptor with "ndr_pull_security_descriptor failed: Range Error", causing chmod to fail with EINVAL.
Change kmalloc() to kzalloc() to ensure the entire buffer is zero-initialized.
[1] https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-dtyp/20233ed8-a6c6-4097-aafa-dd545ed24428
Weakness: CWE-908
Which versions are affected by CVE-2026-46139?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-46139?
Apply the vendor's patch.
Is CVE-2026-46139 being exploited?
There is no known exploitation of CVE-2026-46139 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-46139, DEBIAN-CVE-2026-46139, GHSA-v8jf-78w3-v9hm, ROOT-OS-UBUNTU-2404-CVE-2026-46139, UBUNTU-CVE-2026-46139.