CVE-2026-81038: Zephyr Object Transfer Service OACP checksum uninitialized memory disclosure

CVE-2026-81038 · Severity: high · CVSS 7.1 · Published 2026-10-26

The Zephyr OS Bluetooth Object Transfer Service (OTS) server has a flaw in its checksum calculation response handler that can leak uninitialized stack memory over the air. An attacker within Bluetooth range can send a malformed checksum command to trigger the vulnerability, exposing four random bytes of memory with each request and potentially crashing the device if assertions are enabled. This affects any Zephyr device running OTS without requiring pairing or encryption.

Technologies: Zephyr OS. Vendors: Zephyr.

Quick answers

Is CVE-2026-81038 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-81038 being exploited in the wild.
How severe is CVE-2026-81038?
High severity, with a CVSS score of 7.1, published 26 October 2026.
Which products and versions are affected?
Zephyr OS versions with CONFIG_BT_OTS and Object Transfer Service enabled.
Is there a fix for CVE-2026-81038?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-81038 attacked?
It is attacked from the adjacent network, in an operating system.
Am I affected by CVE-2026-81038?
Check whether you run Zephyr OS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The oacp_ind_send() function in the OTS server appends a Checksum Value field to the response for BT_GATT_OTS_OACP_PROC_CHECKSUM_CALC operations regardless of the result code. On validation failure paths, the response buffer remains uninitialized; invoking net_buf_simple_pull_le32() on the empty buffer discloses four bytes of stack memory on assertion-disabled builds, or triggers a panic on assertion-enabled builds. The OACP characteristic requires no authentication or encryption, allowing any proximate peer to trigger the vulnerability repeatedly by sending Calculate Checksum commands with invalid parameters (e.g., no object selected).

Affected products

  • Zephyr Zephyr OS versions with CONFIG_BT_OTS and Object Transfer Service enabled

Timeline

  • 2026-10-26: disclosed

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