CVE-2026-89637
UnknownSummary
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.
Risk Assessment
Possible kernel use-after-free, which may lead to system crash, memory corruption, or potential privilege escalation via a malicious SMB server.
Recommendation
Update the Linux kernel to a version containing the fix that, when mid->multiRsp is already set, aborts the pending transaction inline (multiEnd, dequeue_mid with malformed=true) without touching buffer pointers.
Other vulnerabilities in Linux kernel (SMB client)
See all- CVE-2026-89636Unknown
In the Linux kernel SMB client, free_tgts() frees all structures in ce->tlist but leaves ce->tgthint pointing to one of the freed cache_dfs_tgt structures. If the pointer is not reset before later use, a use-after-free occurs.
- CVE-2026-89634Unknown
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.
- CVE-2026-89633Unknown
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.
- CVE-2026-89632Unknown
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.
- CVE-2026-89631Unknown
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.
- CVE-2026-46139Medium
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.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2 When a valid primary TRANSACT2 response has been received (mid->resp_buf set, mid->multiRsp true) and a subsequent secondary response causes cifs_check_trans2() to return false -- either because the SMB header is invalid (malformed != 0) or because check2ndT2() rejects the PDU -- handle_mid() overwrites mid->resp_buf with the new buffer (leaking the primary buffer) and, because mid->multiRsp is set, skips the server->smallbuf/bigbuf NULL-out. When the user thread frees mid->resp_buf, server->smallbuf or server->bigbuf is left dangling; the demux thread reuses it for the next packet, resulting in a use-after-free. Combine both early-exit conditions and, when mid->multiRsp is already set, abort the pending transaction inline: set multiEnd, call dequeue_mid() with malformed=true, and return true so handle_mid() exits without touching mid->resp_buf or the server buffer pointers.