VulnerabilityPublished 28 Sep 2026Updated 4 Nov 2026

CVE-2026-18746: zephyrproject zephyr · Memory-safety

Affects zephyrproject zephyrSource CVE Database V5

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Not known to be exploited · CVSS 5.9 Medium : upgrade to 4.5.0 or 4.3.2 when convenient.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score

5.9Medium

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	5.9

EPSS: 0.2% chance of exploitation in 30 days – higher than 18% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.5.0, 4.3.2

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

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

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: None: There is no loss of confidentiality within 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 4.5.0 or 4.3.2.

Affected software

Product	Affected	Fixed in
zephyrprojectzephyr	Affected >=4.4.0 <4.5.0	Fixed in 4.5.0
zephyrprojectzephyr	Affected >=3.7.0 <4.3.2	Fixed in 4.3.2
GitHubzephyr`pkg:github/zephyr`Other threats	Affected >=3.7.0 <4.3.2 >=4.4.0 <4.5.0	Fixed in 4.3.2 4.5.0

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

AI-suggested

This vulnerability is fixed in Zephyr versions 4.3.2 and 4.5.0. Users should upgrade to these or later versions to remediate the issue. No additional mitigation is required as the fix properly validates the context pointer before use.

Description

CVE-2026-18746 is a memory-safety vulnerability in the Zephyr project's LwM2M message handling code. It occurs when processing inbound CoAP WRITE/CREATE requests with a Block1 option, leading to a NULL pointer dereference and device crash. The flaw allows an attacker to cause a fatal memory fault by initiating multiple incomplete block-wise writes, potentially crashing or resetting the device. The vulnerability does not affect confidentiality or integrity. It is fixed in Zephyr versions 4.3.2 and 4.5.0.

Impact

Successful exploitation causes a fatal memory fault leading to device crash or reset (BusFault or corrupted low memory). There is no impact on confidentiality or integrity. The vulnerability requires network access to the LwM2M UDP socket and can be exploited without credentials in NoSec deployments or from lower-trust servers. Legitimate servers performing multiple concurrent block transfers may also trigger this issue accidentally.

Summary

The vulnerability arises in the parse_write_op() function within Zephyr's LwM2M message handling when handling CoAP Block1 transfers. Specifically, for the first block of a transfer, init_block_ctx() is called and may return -ENOMEM while setting the context pointer to NULL if no free block context is available. However, the code immediately stores the block size into the context pointer without verifying it is non-NULL, causing a NULL pointer dereference. An attacker can exploit this by initiating three incomplete block-wise writes and then sending a fourth, triggering the fault. The impact is a fatal memory fault causing device crash or reset. The fix moves the store operation below the NULL check and validates the context pointer before use.

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What to do

Affected software

Description

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

Technical details

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