CVE-2026-31617
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.
Does this matter?
Lower severity and a low EPSS score (0.13%). Track it; it rarely justifies an emergency change on its own.
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 checking") fixed a related class of issues on the host side of NCM.
- CVSS 3.1
- 5.5 MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.13% probability · 3th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-191
- Affected
- linux/linux kernel
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
References
- https://git.kernel.org/stable/c/068a7f2749fff6462a0a908ec415b885fe430f50
- https://git.kernel.org/stable/c/0f156bb5334e588034ca68ac2ee92b23f66e56e7Patch
- https://git.kernel.org/stable/c/1425655c2870054c3ab4712e2b6dbdd331597ada
- https://git.kernel.org/stable/c/6762f8a95772265dd0c2ffe7f400493f3115b135Patch
- https://git.kernel.org/stable/c/74908b0318d1df1188457040b8714ff4d4b68126Patch
- https://git.kernel.org/stable/c/8757a2593631443648218244b9788e193ae0fdc1Patch
- https://git.kernel.org/stable/c/8b3b7bd3c02f98634baaf36c7fc7ac915f6517ca
- https://git.kernel.org/stable/c/8f993d30b95dc9557a8a96ceca11abed674c8acbPatch
- https://git.kernel.org/stable/c/d58ba8f6546232f8414f396c189297dbee03f1a7Patch
- https://access.redhat.com/security/cve/CVE-2026-31617
- https://bugzilla.redhat.com/show_bug.cgi?id=2461448
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31617.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.