CVE-2026-97554 smb: client: avoid using uninitialized SIDs in cifs_posix_to_fattr()
A Linux kernel SMB client flaw allows leaking kernel stack contents to userspace when processing malformed directory entries from an untrusted server.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-97554?
CVE-2026-97554 is a vulnerability in Linux, published on 25 Sep 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: avoid using uninitialized SIDs in cifs_posix_to_fattr()
cifs_posix_to_fattr() ignores the return value of posix_info_parse(). When a malformed POSIX directory entry is encountered (e.g. invalid SID lengths from an untrusted server), posix_info_parse() returns -1 without populating the 'parsed' struct. The uninitialized stack memory in parsed.owner and parsed.group is then passed to sid_to_id(), which processes the garbage bytes and passes them to request_key() to construct a SID string, potentially leaking kernel stack contents to the userspace idmap daemon.
Fix this by checking the return value and skipping the SID-to-id mapping when parsing fails. The remaining fattr fields (timestamps, mode, etc.) are populated directly from the 'info' pointer so they are unaffected.
Which versions are affected by CVE-2026-97554?
How do I fix CVE-2026-97554?
Apply the vendor's patch.
Is CVE-2026-97554 being exploited?
There is no known exploitation of CVE-2026-97554 in the wild and no public exploit code.
Sources
Also known as AZL-104337, BELL-CVE-2026-97554, DEBIAN-CVE-2026-97554, GHSA-vfwc-r92w-jp29, UBUNTU-CVE-2026-97554.