CVE-2026-31617

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb()

The block_len read from the host-supplied NTB header is checked against

ntb_max but has no lower bound. When block_len is smaller than

opts->ndp_size, the bounds check of:

ndp_index > (block_len - opts->ndp_size)

will underflow producing a huge unsigned value that ndp_index can never

exceed, defeating the check entirely.

The same underflow occurs in the datagram index checks against block_len

- opts->dpe_size. With those checks neutered, a malicious USB host can

choose ndp_index and datagram offsets that point past the actual

transfer, and the skb_put_data() copies adjacent kernel memory into the

network skb.

Fix this by rejecting block lengths that cannot hold at least the NTB

header plus one NDP. This will make block_len - opts->ndp_size and

block_len - opts->dpe_size both well-defined.

Commit 8d2b1a1ec9f5 ("CDC-NCM: avoid overflow in sanity c

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References