CVE-2026-90251 Bluetooth: MSFT: validate evt_prefix_len against the response length
A malicious Bluetooth controller can cause the Linux kernel to read uninitialized memory, potentially disclosing sensitive kernel data to the attacker.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90251?
CVE-2026-90251 is a vulnerability in Linux, published on 17 Sep 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:
Bluetooth: MSFT: validate evt_prefix_len against the response length
read_supported_features() only checks that the response covers the fixed part of struct msft_rp_read_supported_features, which is 11 bytes:
if (skb->len < sizeof(*rp)) { bt_dev_err(hdev, "MSFT supported features length mismatch"); goto failed; }
evt_prefix[] is a flexible array member and rp->evt_prefix_len is an unvalidated u8 taken straight out of that response, so
msft->evt_prefix = kmemdup(rp->evt_prefix, rp->evt_prefix_len, GFP_KERNEL);
copies up to 255 bytes from a reply that may have carried none of them. What is copied is data the controller never sent, and it is then used to match incoming vendor events in msft_vendor_evt().
This is not an out-of-bounds access. An skb data allocation always has at least SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) bytes past the payload, which is more than the 255 byte maximum, so the read stays inside the allocation and KASAN does not report it. It is still a read of bytes the host was never given, with the length fully controlled by the controller.
Reject a response that is too short for the prefix it declares.
Verified with an emulated controller over /dev/vhci on a KASAN kernel, with vhci made to advertise an MSFT opcode the way btintel, btqca, btmtk and btrtl do unconditionally. A reply of exactly 11 bytes declaring evt_prefix_len = 255 reaches kmemdup and copies 255 bytes ("skb->len=11 evt_prefix_len=255", with the copied buffer dumped); since the reply ends at the fixed part, all 255 come from past the end of the response. No KASAN report is produced, as expected from the allocation slack described above. With this patch the response is rejected with "MSFT event prefix length mismatch" and msft->evt_prefix is left unset.
Which versions are affected by CVE-2026-90251?
How do I fix CVE-2026-90251?
Apply the vendor's patch.
Is CVE-2026-90251 being exploited?
There is no known exploitation of CVE-2026-90251 in the wild and no public exploit code.
Sources
Also known as AZL-102443, BELL-CVE-2026-90251, DEBIAN-CVE-2026-90251, GHSA-hmjm-jgv8-x76g, UBUNTU-CVE-2026-90251.