UBUNTU-CVE-2026-99115: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fill in FileSysIdentifier in FSPOSIXINFORMATION smb2getinfofilesystem() reports 56 bytes for FSPOSIXINFORMATION, that is the whole of FILESYSTEMPOSIXINFO, but never assigns FileSysIdentifier. Those eight bytes go to the client as they are found in the response buffer. The buffer is zeroed on allocation, so a standalone request leaks nothing. A compound request can leak: the offset of the next response is advanced by the length pinned for the previous one, so a reply that was written into the buffer and then dropped in favour of the short error response of smb2seterrrsp() stays there, and the next reply is laid over it with only the header cleared. Report the file system id statfs() returned, which is what the field is for. FileSysIdentifier is le64 and ffsid is a pair of ints, so assemble the value first, val[0] as the low half, and convert it on the way out.
Affected Software
Event History
Frequently Asked Questions
When can this disclose data to an SMB client?
The leak requires a compound SMB request. A standalone FS_POSIX_INFORMATION request does not leak data because the response buffer is zeroed when allocated.
What must an attacker be able to do to trigger the issue?
An attacker needs to send SMB requests to ksmbd and construct a compound request that causes an earlier reply to be replaced by a short error response, leaving prior response-buffer contents available in the next FS_POSIX_INFORMATION reply.
What data may be exposed?
The unassigned eight-byte FileSysIdentifier field can contain residual data from an earlier response written into the same compound-request response buffer. The fix populates this field with the filesystem identifier returned by statfs().