# 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.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Aug 2026
- **Updated:** 13 Aug 2026
- **Also known as:** GHSA-483r-jq2x-5cp9

## 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 (Loop with Unreachable Exit Condition)

## 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.

## Is CVE-2026-12236 being exploited?

There is no known exploitation of CVE-2026-12236 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12236 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-12236 in the wild and no public exploit code.

Affected product: zephyrproject zephyr. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-12236/ (Markdown: https://insights.sbomify.com/CVE-2026-12236/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12236
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12236
- OSV: https://osv.dev/vulnerability/CVE-2026-12236

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-12236/
Summaries are generated and may contain mistakes; the official description above is the record.