CVE-2025-39942

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No local access is needed \u2014 a single crafted RDMA send from a remote peer reaches the vulnerable code.\nAC:L - `remaining_data_length` is a plain header field the attacker writes directly, and the attacker also controls `preferred_send_size` in the SMB Direct negotiate request that determines `max_fragmented_recv_size`, so the unsatisfiable-reassembly condition is set up deterministically with two packets. No race, no memory-layout grooming, no timing dependency.\nPR:N - `recv_done()` is transport-level code that runs on every data transfer message before any SMB2 session setup or credential verification, and ksmbd never validates the negotiate request's `preferred_send_size`, letting an unauthenticated peer shrink the reassembly capacity below the pre-auth `SMB3_MAX_MSGSIZE` PDU limit and wedge the connection thread with no credentials at all.\nUI:N - The server processes the malformed data transfer message automatically as part of normal SMB Direct receive completion handling. No administrator or user action on the target is involved.\nS:U - The impact is confined to the ksmbd server's own kernel context \u2014 the stalled connection thread and pinned kernel allocations \u2014 with no crossing into a different security authority such as a hypervisor or IOMMU boundary.\nC:N - With the parent commit's `data_offset`/`data_length` validation in place, every `memcpy()` source in `smb_direct_read()` stays within the DMA'd `wc->byte_len` region, so no out-of-bounds or stale buffer contents are read and nothing is disclosed to the attacker beyond data they supplied themselves.\nI:N - The unsigned overflow of `data_length + remaining_data_length` only desynchronizes RFC1002 PDU framing on a byte stream the attacker already fully controls, and `get_rfc1002_len()`'s `0xFFFFFF` mask plus the `max_allowed_pdu_size` check prevent any under-allocation or out-of-bounds write, so no kernel data or control flow is modified.\nA:H - A remote peer can request reassembly of a message larger than the transport can ever hold (bounded by 255 recvmsg buffers), permanently blocking the ksmbd connection kthread in `wait_event_interruptible()` while it pins a multi-megabyte `kvmalloc` buffer and the entire receive buffer pool; repeating this across connections exhausts kernel memory and server threads, denying SMB service."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/server/transport_rdma.c"], "versions": [{"version": "2ea086e35c3d726a3bacd0a971c1f02a50e98206", "lessThan": "196a3a7676d726ee67621ea2bf3b7815ac2685b4", "status": "affected", "versionType": "git"}, {"version": "2ea086e35c3d726a3bacd0a971c1f02a50e98206", "lessThan": "d3cb3f209d35c44b7ee74f77ed27ebb28995b9ce", "status": "affected", "versionType": "git"}, {"version": "2ea086e35c3d726a3bacd0a971c1f02a50e98206", "lessThan": "9644798294c7287e65a7b26e35aa6d2ce3345bcc", "status": "affected", "versionType": "git"}, {"version": "2ea086e35c3d726a3bacd0a971c1f02a50e98206", "lessThan": "c64b915bb3d9339adcae5db4be2c35ffbef5e615", "status": "affected", "versionType": "git"}, {"version": "2ea086e35c3d726a3bacd0a971c1f02a50e98206", "lessThan": "e1868ba37fd27c6a68e31565402b154beaa65df0", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/server/transport_rdma.c"], "versions": [{"version": "5.15", "status": "affected"}, {"version": "0", "lessThan": "5.15", "status": "unaffected", "versionType": "semver"}, {"version": "6.1.154", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.6.108", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.49", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.16.9", "lessThanOrEqual": "6.16.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.17", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "6.1.154"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "6.6.108"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "6.12.49"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "6.16.9"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "6.17"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/196a3a7676d726ee67621ea2bf3b7815ac2685b4"}, {"url": "https://git.kernel.org/stable/c/d3cb3f209d35c44b7ee74f77ed27ebb28995b9ce"}, {"url": "https://git.kernel.org/stable/c/9644798294c7287e65a7b26e35aa6d2ce3345bcc"}, {"url": "https://git.kernel.org/stable/c/c64b915bb3d9339adcae5db4be2c35ffbef5e615"}, {"url": "https://git.kernel.org/stable/c/e1868ba37fd27c6a68e31565402b154beaa65df0"}], "title": "ksmbd: smbdirect: verify remaining_data_length respects max_fragmented_recv_size", "x_generator": {"engine": "bippy-1.2.0"}}}}

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{"bugzilla": {"description": "ksmbd: smbdirect: verify remaining_data_length respects max_fragmented_recv_size", "id": "2401421", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2401421"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.5", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "status": "draft"}, "details": ["In the Linux kernel, the following vulnerability has been resolved:\nksmbd: smbdirect: verify remaining_data_length respects max_fragmented_recv_size\nThis is inspired by the check for data_offset + data_length."], "name": "CVE-2025-39942", "public_date": "2025-10-04T07:31:04Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2025-39942\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-39942\nhttps://git.kernel.org/stable/c/196a3a7676d726ee67621ea2bf3b7815ac2685b4\nhttps://git.kernel.org/stable/c/9644798294c7287e65a7b26e35aa6d2ce3345bcc\nhttps://git.kernel.org/stable/c/c64b915bb3d9339adcae5db4be2c35ffbef5e615\nhttps://git.kernel.org/stable/c/d3cb3f209d35c44b7ee74f77ed27ebb28995b9ce\nhttps://git.kernel.org/stable/c/e1868ba37fd27c6a68e31565402b154beaa65df0\nhttps://lore.kernel.org/linux-cve-announce/2025100419-CVE-2025-39942-0297@gregkh/T"]}

{"created": "2025-10-06T14:41:55.426343+00:00", "updated": "2025-10-06T14:41:55.426439+00:00", "vendors": ["linux", "linux$PRODUCT$linux_kernel"]}