VulnerabilityPublished 28 Sep 2026Updated 4 Nov 2026

CVE-2026-18747: zephyrproject zephyr · Integer Overflow

Affects zephyrproject zephyrSource CVE Database V5

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Not known to be exploited · CVSS 6.8 Medium : upgrade to 4.4.2 or 4.3.2 when convenient.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score

6.8Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (zephyr)	CVSS 3.1	6.8

EPSS: 0.2% chance of exploitation in 30 days – higher than 15% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.4.2, 4.3.2

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

Attack Vector: Local
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: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
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 28 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 13 Nov 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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

Upgrade zephyrproject zephyr to 4.4.2 or 4.3.2.

Affected software

Product	Affected	Fixed in
zephyrprojectzephyr	Affected >=4.4.0 <4.4.2	Fixed in 4.4.2
zephyrprojectzephyr	Affected >=1.11.0 <4.3.2	Fixed in 4.3.2
GitHubzephyr`pkg:github/zephyr`Other threats	Affected >=1.11.0 <4.3.2 >=4.4.0 <4.4.2	Fixed in 4.3.2 4.4.2

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

AI-suggested

A fix is available in Zephyr versions 4.3.2 and 4.4.2 that prevents the integer underflow by rejecting packet lengths of two bytes or fewer. Users should upgrade to these or later versions to remediate the vulnerability. No additional mitigations are required as the flaw is addressed by the official fix.

Description

CVE-2026-18747 is an integer overflow vulnerability in the Zephyr project's MCUmgr SMP-over-console transport. It arises from improper handling of packet length fields during base64 frame decoding, leading to an underflow and an inflated buffer length. This allows out-of-bounds reads and potential denial of service or memory disclosure via unauthenticated console input. The flaw affects Zephyr versions from 1.11.0 up to but not including 4.3.2, and from 4.4.0 up to but not including 4.4.2. A fix is available in versions 4.3.2 and 4.4.2 that rejects packet lengths of two bytes or fewer to prevent underflow.

Impact

An unauthenticated attacker with write access to the MCUmgr management console can trigger an integer underflow that leads to out-of-bounds reads. This can cause denial of service by faulting the MCUmgr thread and may allow memory disclosure due to improper CBOR decoding of attacker-controlled data. The vulnerability does not increase integrity risks beyond the unauthenticated transport's existing limitations.

Summary

The vulnerability exists in the MCUmgr SMP-over-console transport of Zephyr, specifically in the function mcumgr_serial_process_frag() where a 16-bit packet length is read and the trailing CRC is unconditionally stripped, causing an underflow when the declared length is 0 or 1. This underflow inflates the buffer length to approximately 65 KB, far exceeding the actual buffer size (default 384 bytes). An attacker with write access to the management console (e.g., USB CDC-ACM port) can send a crafted 7-byte frame that triggers this condition without authentication or prior session state. The inflated length causes the CBOR decoder to read beyond buffer bounds, potentially leading to denial of service or memory disclosure through the OS echo handler. The vulnerability is fixed by rejecting packet lengths of two bytes or fewer in mcumgr_serial_extract_len(), preventing the underflow. The test-only loopback transport retains the pattern but is not exposed externally.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2026, 11:28 UTC

Technical details

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