CVE-2026-89641
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk4th percentile - higher than 4% of all known CVEs
Summary
In the Linux kernel, cifs_file_set_size() has a use-after-free. When the else branch finds a writable file handle via find_writable_file(), it borrows tcon and server from the handle, attempts the handle-based set_file_size() RPC, then releases the handle with cifsFileInfo_put(). If set_file_size() fails, execution falls through to the path-based fallback, which reuses the borrowed tcon and server even though cifsFileInfo_put() may have freed tcon. The fix sets tcon = NULL after cifsFileInfo_put() to force the safe cifs_sb_tlink() path.
Risk Assessment
A use-after-free in the kernel CIFS client can lead to system crash or arbitrary code execution in kernel context. It requires file operations on a CIFS/SMB share.
Recommendation
Update the Linux kernel to a version containing this fix. Avoid file resize operations on CIFS shares on unpatched systems.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: cifs: clear tcon after cifsFileInfo_put() in cifs_file_set_size() When the else branch of cifs_file_set_size() finds a writable file handle via find_writable_file(), it borrows tcon and server from the handle's tlink, attempts the handle-based set_file_size() RPC, and then releases the handle with cifsFileInfo_put(). If set_file_size() fails, execution falls through to the path-based fallback, which reuses the borrowed tcon and server under the "if (tcon == NULL)" guard. Since tcon is not NULL at that point, the guard is skipped. If cifsFileInfo_put() dropped the last reference on a tlink that was already removed from the tlink tree (TCON_LINK_IN_TREE cleared, as happens during reconnection or session teardown), cifs_put_tlink() will have freed tcon; the subsequent set_path_size() call is then a use-after-free. Setting tcon = NULL after cifsFileInfo_put() causes the existing guard to take the cifs_sb_tlink() path, which acquires a fresh reference for the path-based operation or fails cleanly if the session is gone.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS