# CVE-2026-81038: Bluetooth OTS server discloses uninitialized stack memory in failed Calculate Checksum responses


- **Severity:** High 7.1 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 26 Oct 2026
- **Updated:** 26 Oct 2026
- **Also known as:** GHSA-7c9w-mhqw-5g86, UBUNTU-CVE-2026-81038

## What is CVE-2026-81038?

CVE-2026-81038 is a high-severity vulnerability in zephyrproject zephyr, published on 26 Oct 2026. 

### Official description

The Object Transfer Service server builds its Object Action Control Point (OACP) response indication in oacp_ind_send() (subsys/bluetooth/services/ots/ots_oacp.c). Before this fix the four-byte Checksum Value field was appended whenever the requested op code was BT_GATT_OTS_OACP_PROC_CHECKSUM_CALC, regardless of the result code. The response payload is a bare, uninitialized four-byte stack buffer declared with NET_BUF_SIMPLE_DEFINE(resp_param, sizeof(uint32_t)) in bt_gatt_ots_oacp_write(), and it is filled only on the success path of oacp_checksum_proc_validate(). On every failure path the buffer is still empty, so net_buf_simple_pull_le32() was invoked on a zero-length buffer.

The OACP characteristic and its client characteristic configuration descriptor are declared with BT_GATT_PERM_WRITE and BT_GATT_PERM_READ | BT_GATT_PERM_WRITE, so no pairing, encryption, or authentication is required. Any peer within radio range that can connect to a device running the OTS server can enable OACP indications and write a nine-byte Calculate Checksum command that fails validation — for example by issuing it with no object selected, which returns BT_GATT_OTS_OACP_RES_INV_OBJ. Because oacp_command_decode() accepts the Calculate Checksum op code unconditionally (it is not guarded by CONFIG_BT_OTS_OACP_CHECKSUM_SUPPORT), builds without checksum support are reachable too: they answer BT_GATT_OTS_OACP_RES_OPCODE_NOT_SUP and take the same bad path.

On builds with CONFIG_ASSERT enabled, the zero-length pull trips the assertion inside net_buf_simple_pull_mem() and panics the device, giving a remotely triggered denial of service. On builds with assertions disabled there is no check: the pull returns the untouched stack array and four bytes of uninitialized stack memory are copied into the indication and transmitted to the peer, repeatable on every request. The disclosure is bounded to four bytes per request and the write stays inside the seven-byte res indication buffer, so there is no memory corruption; the impact is uninitialized-memory disclosure plus an availability loss in assertion-enabled configurations.

Weakness: CWE-908 (Use of Uninitialized Resource), CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-81038?


## How do I fix CVE-2026-81038?

No fix has been published for CVE-2026-81038 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-81038 being exploited?

There is no known exploitation of CVE-2026-81038 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81038 and fix it if it is affected.

What it is: CVE-2026-81038 is a high-severity vulnerability in zephyrproject zephyr, published on 26 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-81038 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-2026-81038/ (Markdown: https://insights.sbomify.com/CVE-2026-81038/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81038
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81038
- OSV: https://osv.dev/vulnerability/CVE-2026-81038

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81038/
Summaries are generated and may contain mistakes; the official description above is the record.