VulnerabilityPublished 4 Nov 2026

CVE-2026-87043: zephyrproject zephyr · Crypto

Affects zephyrproject zephyrSource CVE Database V5

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Not known to be exploited · CVSS 4.8 Medium : upgrade to 4.5.0 when convenient.

Data as of 4 Nov 2026, 06:28 UTC

CVSS 3.1 base score

4.8Medium

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	4.8

Patch: Available – fixed in 4.5.0

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

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

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: 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: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Nov 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 3 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.

Affected software

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

A fix is available in Zephyr version 4.5.0 that corrects the early return behavior and ensures fallback random sources are used when the entropy device is not ready. Users should upgrade to version 4.5.0 or later to remediate this issue. No additional mitigation is required as the cryptographic random path is unaffected and the vendor has provided an official fix.

Description

CVE-2026-87043 is a vulnerability in the Zephyr project's entropy-device random number generator where an early return on device unavailability causes the system to return stale or uninitialized memory as random data. This affects non-cryptographic random values used in various network protocols and system components, potentially leaking sensitive memory contents. The issue is fixed in Zephyr version 4.5.0.

Impact

Non-cryptographic random values generated by the system may be constant or contain stale memory contents, leading to predictable or repeated values in network protocols and system security features. This can disclose sensitive memory contents over the network and degrade protocol security. The cryptographically secure random number generation remains intact. There is no known exploit in the wild, and an attacker cannot induce the device unready state but can observe and exploit the resulting non-random values remotely on affected devices.

Summary

The entropy-device random number generator in Zephyr's subsys/random/random_entropy_device.c returns early with an error code when the device is not ready, before reaching the fallback timer-based random source. Because the public sys_rand_get() syscall discards errors and returns void, the caller's buffer remains unmodified, resulting in stale or uninitialized memory being returned as random data. This affects non-cryptographic random values such as CoAP tokens, TCP initial sequence numbers, DHCP transaction IDs, WebSocket masking keys, RTP SSRCs, and pointer authentication keys. The flaw occurs during normal runtime conditions when entropy drivers are not yet initialized or fail to initialize. The fix in version 4.5.0 ensures the fallback timer source is used when the device is not ready, preventing stale data from being returned. The cryptographically secure random path remains unaffected.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2026, 06:16 UTC

Technical details

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