{"id":"CVE-2026-97559","summary":"smb: client: fail DACL rewrite when the new DACL exceeds 64K","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fail DACL rewrite when the new DACL exceeds 64K\n\nreplace_sids_and_copy_aces() and set_chmod_dacl() accumulate the size of\nthe DACL they build in a u16. That accumulator can wrap.\n\nvalidate_dacl() caps num_aces at (dacl_size - sizeof(struct smb_acl)) /\n20, i.e. 3276 for a maximally sized DACL, while each rewritten ACE can\ngrow to sizeof(struct smb_ace) (76 bytes) once its SID is replaced with\none carrying SID_MAX_SUB_AUTHORITIES sub-authorities. The worst case is\ntherefore sizeof(struct smb_acl) + 3276 * 76 = 248984 bytes, far beyond\nwhat a u16 can hold. A wraparound is reached with 863 ACEs.\n\nAfter the wraparound, ndacl_ptr-\u003esize becomes meaningless and the offset\nwill point anywhere in the ACE array. As a result, we will see\ncorruption of the DACL, which then gets sent to the server. This is not\nan out-of-bounds write as the allocation now covers the worst-case\nexpansion, so writes will always go into the buffer.\n\nAdjust the code to use a u32 internally and return -EOVERFLOW in the\noverflow case. The operation must be refused, because a DACL can only\nhold 2^16-1 bytes on the wire and larger DACLs cannot be represented.\n\nset_chmod_dacl() carries the same pattern and is fixed the same way. It\nonly wraps once the source DACL comes within roughly 380 bytes of the\n64K ceiling, but the failure mode is identical.","modified":"2026-09-26T03:48:27.680743982Z","published":"2026-09-25T10:21:48.866Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97559.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2ef532a01f44687f5b95001e88247cf05bff9892"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d05045177a855386bca5e1909e08d06290e6e3b3"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ee13d687d06a6fbb2008625dd560c654231b28e0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97559.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-97559"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"f5065508897a922327f32223082325d10b069ebc"},{"fixed":"2ef532a01f44687f5b95001e88247cf05bff9892"},{"fixed":"ee13d687d06a6fbb2008625dd560c654231b28e0"},{"fixed":"d05045177a855386bca5e1909e08d06290e6e3b3"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97559.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.12.0"},{"fixed":"6.18.53"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.7"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97559.json"}}],"schema_version":"1.9.0"}