VulnerabilityPublished 26 Oct 2026

CVE-2026-81038: zephyrproject zephyr · Info-leak

Affects zephyrproject zephyrSource CVE Database V5

Not known to be exploited · CVSS 7.1 High.

Data as of 26 Oct 2026, 18:13 UTC

CVSS 3.1 base score

7.1High

How severe the flaw is on the 0–10 CVSS scale.

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Attack Vector: Adjacent
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Adjacent: The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 26 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
zephyrprojectzephyr	Affected >=3.3.0 <=4.4.2	Fixed in–
GitHubzephyr`pkg:github/zephyr`Other threats	Affected >=3.3.0 <=4.4.2	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Until a fix is available, restricting physical or radio access to the device may reduce exposure. Monitoring for vendor updates and applying official patches when released is recommended.

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.

Impact

An unauthenticated attacker within radio range can connect to a vulnerable Zephyr OTS server and repeatedly request checksum calculations that fail validation, causing the server to disclose four bytes of uninitialized stack memory per request. This information leak could potentially expose sensitive data residing on the stack. On builds with assertions enabled, the vulnerability can cause the device to panic and become unavailable, resulting in a denial of service. There is no known memory corruption or code execution impact. The CVSS v3.1 score is 7.1 (High), reflecting local network attack vector, low attack complexity, no privileges required, no user interaction, confidentiality impact, and high availability impact.

Summary

The vulnerability exists in the OTS server's handling of the OACP response indication in Zephyr. Specifically, when processing the Calculate Checksum opcode (BT_GATT_OTS_OACP_PROC_CHECKSUM_CALC), the server appends a four-byte Checksum Value field regardless of the operation's success. The buffer used for this field is a four-byte uninitialized stack array that is only properly filled on successful checksum validation. On failure paths, the buffer remains uninitialized, and the code reads and transmits these uninitialized bytes to the requesting peer. Because the OACP characteristic requires no pairing, encryption, or authentication, any peer within radio range can exploit this to obtain four bytes of uninitialized stack memory per request. Additionally, builds with assertions enabled will panic due to an assertion failure, causing a remotely triggered denial of service. The flaw does not cause memory corruption but results in information disclosure and potential availability impact.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 16:36 UTC

Technical details

References

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