VulnerabilityPublished 13 Aug 2021Updated 30 May 2025

CVE-2021-31399: On 2N Access Unit 2.0 2.31.0.40.5 devices, an attacker can pose as the web relay for a

Source CVE Database V5

Not known to be exploited · CVSS 4.6 Medium.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

4.6Medium

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

EPSS: 0.8% chance of exploitation in 30 days – higher than 57% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

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

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

Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
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).
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.
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.
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.
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.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 2021
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
n/a n/a	Affected =2.31.0.40.5	Fixed in–

AI-suggested

Network Segmentation: Isolate 2N Access Unit devices on dedicated VLANs or network segments with strict access controls to limit attacker proximity.
Use Encrypted Communication: Ensure that all communications with the access control devices use strong encryption protocols (e.g., HTTPS with valid certificates) to prevent interception or impersonation of web relays.
4. Monitor Network Traffic: Implement network monitoring to detect unusual traffic patterns or attempts to impersonate devices within the local network. 5. User Awareness: Train users to recognize suspicious prompts or interactions that could facilitate MITM attacks, reducing the risk from required user interaction. 6. Access Control Hardening: Limit administrative access to the devices and use multi-factor authentication where possible to reduce the impact of intercepted credentials. 7. Incident Response Planning: Prepare for potential access control disruptions by having contingency plans to maintain physical security if devices are compromised.

Description

On 2N Access Unit 2.0 2.31.0.40.5 devices, an attacker can pose as the web relay for a man-in-the-middle attack.

Impact

For European organizations, especially those using 2N Access Unit devices for physical access control, this vulnerability could lead to unauthorized interception of access control communications. This might allow attackers to disrupt access control operations, potentially causing denial of service or unauthorized monitoring of access events. Confidentiality of access logs or user credentials transmitted via the web relay could be compromised, increasing the risk of targeted attacks or social engineering. Organizations in sectors with high physical security requirements—such as government, critical infrastructure, finance, and transportation—may face operational disruptions and increased risk of physical breaches. The requirement for user interaction and adjacency limits remote exploitation but does not eliminate risk in environments where attackers can gain network proximity, such as through compromised internal devices or guest networks. The absence of known exploits suggests limited active threat but also underscores the importance of proactive mitigation to prevent future exploitation.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 8 Jul 2025, 15:28 UTC

Technical details

References

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