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CVE-2026-31709 is a memory-safety vulnerability in the Linux kernel SMB client, specifically in the cifsacl code in fs/smb/client/cifsacl.c. The flaw arises because server-supplied Discretionary Access Control List (DACL) data was not fully structurally validated before being reused to rebuild chmod/chown security descriptors. In the affected logic, build_sec_desc() and id_mode_to_cifs_acl() derive a DACL pointer from a server-controlled dacloffset and then process the incoming ACL. Although an earlier check ensured that the smb_acl header itself fit before reading fields such as size and num_aces, the code still allowed rewrite helpers to iterate ACEs based on num_aces without validating that the full DACL body and each claimed ACE were within bounds. A malicious SMB server can therefore return a truncated DACL with a valid header and forged ACE count, causing helpers such as replace_sids_and_copy_aces() and set_chmod_dacl() to read or copy past the validated extent while handling attacker-controlled ACE data. The upstream fix introduced a shared validate_dacl() routine, added per-ACE bounds validation, and reused the same validator in parse_dacl() so both parsing and rewrite paths enforce the same well-formedness checks.
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A Linux kernel SMB client vulnerability in cifsacl involving validation of the whole DACL before rewriting it.
A Linux kernel SMB client cifsacl input-validation flaw where a malicious SMB server can supply a malformed DACL with inconsistent ACE counts, causing out-of-bounds read/copy and memory corruption that may lead to information disclosure or denial of service.
Linux kernel SMB client vulnerability in cifsacl related to validating the whole DACL before rewriting it.
Linux kernel SMB client vulnerability in cifsacl related to validating the whole DACL before rewriting it.
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Cross-references every affected SKU, including bundled OEM variants.
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