CVE-2026-31617 usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb()
A malicious USB host can trigger an integer underflow in the Linux kernel NCM gadget driver, leading to out-of-bounds memory reads and potential code execution.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31617?
CVE-2026-31617 is a medium-severity vulnerability in Linux kernel, published on 24 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-191
Which versions are affected by CVE-2026-31617?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31617?
Apply the vendor's patch.
Is CVE-2026-31617 being exploited?
There is no known exploitation of CVE-2026-31617 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31617, DEBIAN-CVE-2026-31617, GHSA-v24g-wpq8-cwqx, ROOT-OS-DEBIAN-11-CVE-2026-31617, ROOT-OS-DEBIAN-12-CVE-2026-31617, ROOT-OS-DEBIAN-13-CVE-2026-31617 and 3 more.