CVE-2026-89636

In the Linux kernel SMB client, cifs_check_trans2() returning false for a malformed secondary T2 response (invalid SMB header or PDU rejected by check2ndT2()) causes handle_mid() to overwrite mid->resp_buf with the new buffer, leaking the primary buffer and leaving server->smallbuf/bigbuf dangling. This results in a use-after-free when the demux thread reuses the freed buffer.

In the Linux kernel SMB client, the ALIGN() macro in symlink_data() can overflow for ErrorDataLength values near UINT32_MAX (e.g. 0xFFFFFFF9), wrapping to 0. This causes the bounds check to pass and the loop to advance by zero bytes, leaving pointer 'p' pointing into stale data.

In the Linux kernel SMB client, coalesce_t2() computes data pointers directly from server-supplied DataOffset fields without validating them against buffer bounds. A small DataOffset can push a pointer below the data area and overwrite header fields, while a large one can push it past the buffer end, causing out-of-bounds heap reads or writes.

In the Linux kernel SMB client, CIFSTCon() bounds its strnlen() by the server's ByteCount minus two, which for ByteCount 0 or 1 becomes negative as an int and converts to a huge size_t. The later subtraction wraps __u16 bytes_left, allowing cifs_strndup_from_utf16() to read up to 65535 bytes from a ~16 KB object, leaking data through /proc/fs/cifs/DebugData.

In the Linux kernel SMB client, the fallocate emulation for small interior ranges (mode 0 / FALLOC_FL_KEEP_SIZE) issued FSCTL_QUERY_ALLOCATED_RANGES without first flushing data. Contrary to Win32 documentation, this query is not coherent with recently written data, so the server could report a written range as unallocated and the emulation overwrote live data with zeroes. The issue affects Windows servers; Samba does not exhibit this behavior.

In the Linux kernel SMB client, smb3_insert_range() and smb3_collapse_range() failed to properly invalidate the page cache when the offset or old EOF was not page-aligned. Boundary pages were only partially zeroed and remained uptodate, so the client could return stale data after a successful insert/collapse range operation.

In the Linux kernel SMB client, reparse_buf_ptr() reads the ReparseDataLength field before verifying that the received data covers the full fixed header. If a server returns OutputCount < 6, the read at offset 4-5 reaches past the end of the received data.

A vulnerability has been identified in the Linux kernel SMB client related to improper initialization of the security descriptor buffer. A change in the data structure caused the reserved field to remain uninitialized, leading to errors when attempting to use chmod.