CVE-2026-89633
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk41th percentile - higher than 41% of all known CVEs
Summary
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.
Risk Assessment
Possible out-of-bounds heap read or write triggered by a malicious or faulty SMB server, which may lead to kernel memory corruption or privilege escalation.
Recommendation
Update the Linux kernel to a version containing the fix that adds lower- and upper-bound checks for both data pointers before the memcpy and before modifying header fields.
Other vulnerabilities in Linux kernel (SMB client)
See all- CVE-2026-89637Critical
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.
- CVE-2026-89636Critical
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-2026-89634Critical
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-2026-89631Critical
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-2026-98684Low risk· EPSS 5%
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.
- CVE-2026-98125Medium
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.
- CVE-2026-89632High
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-2026-46139Medium
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 OOB read/write from unvalidated DataOffset in coalesce_t2() coalesce_t2() computes data pointers directly from server-supplied DataOffset fields with no validation against buffer bounds: data_area_of_tgt = (char *)&pSMBt->hdr.Protocol + get_unaligned_le16(&pSMBt->t2_rsp.DataOffset); data_area_of_src = (char *)&pSMBs->hdr.Protocol + get_unaligned_le16(&pSMBs->t2_rsp.DataOffset); data_area_of_tgt += total_in_tgt; ... memcpy(data_area_of_tgt, data_area_of_src, total_in_src); A small DataOffset can push a pointer below the actual byte area, overwriting header fields; a large one can push it past the buffer end, causing out-of-bounds heap reads (source) or writes (target). The BCC overflow guard does not prevent this: BCC reflects how much data is present, while DataOffset controls where in the buffer it starts. The "validate target area" comment present since the function was first written in 2005 was a placeholder that was never implemented. Add lower- and upper-bound checks for both data pointers before the memcpy, and before any target header fields are modified.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS