CVE-2026-64403 Bluetooth: L2CAP: validate option length before reading conf opt value
A missing length validation in the Linux kernel Bluetooth L2CAP module allows out-of-bounds reads, potentially causing a denial of service.
- 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-2026-64403?
CVE-2026-64403 is a high-severity vulnerability in Linux kernel, published on 25 Jul 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: L2CAP: validate option length before reading conf opt value
l2cap_get_conf_opt() derives the option length from the attacker-controlled opt->len field and immediately dereferences opt->val (as u8, get_unaligned_le16() or get_unaligned_le32(), or a raw pointer for the default case) before any caller has confirmed that opt->len bytes are present in the buffer. The callers (l2cap_parse_conf_req(), l2cap_parse_conf_rsp() and l2cap_conf_rfc_get()) only detect a malformed option afterwards, once the running length has gone negative, by which point the out-of-bounds read has already executed.
An existing post-hoc length check keeps the garbage value from being consumed, so this is not a data leak in the current control flow. It is still a validate-after-use ordering bug: up to 4 bytes are read past the end of the buffer before it is known to contain them, and it is fragile to future changes in the callers.
Fix it at the source. Pass the end of the buffer into l2cap_get_conf_opt() and refuse to touch opt->val unless the full option (header + value) fits. Each caller computes an end pointer once before the loop and checks the return value directly instead of inferring the error from a negative length.
Which versions are affected by CVE-2026-64403?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-64403?
Apply the vendor's patch.
Is CVE-2026-64403 being exploited?
There is no known exploitation of CVE-2026-64403 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-93704, BELL-CVE-2026-64403, DEBIAN-CVE-2026-64403, GHSA-wqwg-v9cc-cpq7, ROOT-OS-DEBIAN-12-CVE-2026-64403, ROOT-OS-UBUNTU-2204-CVE-2026-64403 and 1 more.