CVE-2025-39933

Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source

AV:NAttack vector, network

The vulnerable code parses `smbdirect_data_transfer` headers received directly from a remote SMB server over RDMA, and iWARP/RoCEv2 are routable over ordinary IP networks (soft-iWARP/soft-RoCE need no special hardware). A malicious, compromised, or spoofed SMB Direct peer reaches `recv_done()` purely over the network.

AC:LAttack complexity, low

The attacker writes `data_offset`/`data_length` as plain header fields in a single crafted data-transfer message; there is no race, no memory-layout precondition, and the out-of-bounds read is deterministic and repeatable at an offset of the attacker's choosing.

PR:NPrivileges required, none

`recv_done()` switches to `SMBDIRECT_EXPECT_DATA_TRANSFER` as soon as the unauthenticated transport-level SMBD negotiate completes, so the malformed packet is processed before SMB2 NEGOTIATE/SESSION_SETUP and before any signing or encryption is established — the peer needs no credentials on the client.

UI:NUser interaction, none

Once an SMB Direct mount exists (including automounts, fstab, DFS referrals, and automatic reconnects), a hostile or compromised server can send the crafted frame at any time and the client processes it automatically in its receive-completion and demultiplex paths. No administrator or user action is required at the moment of attack.

S:UScope, unchanged

The out-of-bounds access, the disclosed data, and the resulting fault are all confined to the client kernel's own security authority; no hypervisor, IOMMU, or sandbox boundary is crossed.

C:HConfidentiality impact, high

The unvalidated 32-bit `data_offset` makes `copy_to_iter()` read from an attacker-chosen address up to 4 GiB past a ~2 KB receive-buffer slab object, and the inflated `data_length` keeps that buffer at the queue head so `offset` advances on each call — allowing a remote peer to stream out large amounts of kernel memory, which is then delivered to userspace as SMB response/file content.

I:LIntegrity impact, low

There is no out-of-bounds write, but the client assembles and parses SMB2 responses built from out-of-bounds kernel memory, so connection state, file metadata, and page-cache contents returned to applications are driven by data the attacker caused the kernel to read from outside the intended buffer.

A:HAvailability impact, high

A large `data_offset` faults on unmapped memory or a vmalloc guard page in the demultiplex/softirq path, and an inflated `data_length` desynchronizes `reassembly.data_length` so `_get_first_reassembly()` returns NULL and is immediately dereferenced — either way an oops (full panic with `panic_on_oops`) that tears down the mount.