CVE-2026-12236 Infinite loop (DoS) in Bluetooth GATT client parsing of Read-By-Type responses with zero data length
An unauthenticated adjacent attacker can cause a denial of service in Zephyr RTOS by sending a malformed Bluetooth GATT response that triggers an infinite loop.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-12236?
CVE-2026-12236 is a medium-severity denial of service vulnerability in zephyrproject zephyr, published on 13 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
The Bluetooth host GATT client function parse_read_std_char_desc() in subsys/bluetooth/host/gatt.c parses an ATT Read By Type Response received from a remote GATT server during BT_GATT_DISCOVER_STD_CHAR_DESC discovery. The per-entry stride rsp->len is taken directly from the peer's PDU, and the parse loop both tests its exit condition (length >= rsp->len) and advances (length -= rsp->len, pdu += rsp->len) using that value. The minimum value of rsp->len was never validated before the loop.
A malicious or malfunctioning peer can reply with rsp->len = 0. Because length is unsigned and never decreases, the loop condition stays true forever and the read pointer never advances; as long as the body is at least a few bytes with a non-zero handle and a matching descriptor UUID, the host repeatedly re-parses the same bytes and invokes the discovery callback, never terminating. This hangs the Bluetooth host processing thread (CWE-835, loop with unreachable exit condition).
The condition is reachable by any connected peer once the local device initiates standard-descriptor-value discovery; GATT discovery does not require bonding or encryption, so an unauthenticated adjacent attacker that the device connects to can trigger it. The impact is denial of service of the Bluetooth subsystem (and likely a watchdog reset on constrained targets); there is no memory disclosure or corruption.
The fix adds a rsp->len < sizeof(struct bt_att_data) check before the loop, rejecting under-length responses so the stride is always non-zero and the loop terminates. The sibling parsers parse_include() and parse_characteristic() already validated rsp->len and are unaffected.
Weakness: CWE-835
Which versions are affected by CVE-2026-12236?
How do I fix CVE-2026-12236?
No fix has been published for CVE-2026-12236 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-12236 being exploited?
There is no known exploitation of CVE-2026-12236 in the wild and no public exploit code.
Sources
Also known as GHSA-483r-jq2x-5cp9.