Security Resilience

CVE-2023-25556

Auth Bypass in Schneider-Electric Merten Tasterschnittstelle 4Fach Plus Firmware 1.0 … 1.2

Published
18 April 2023
Modified
21 November 2024
Patch / advisory
CVSS Score v3.1 8.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
EPSS Score 0.0036 28th percentile
Risk Priority 61 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2023-25556 is a high-severity Improper Authentication (CWE-287) vulnerability in Schneider-Electric Merten Tasterschnittstelle 4Fach Plus Firmware. Its CVSS base score is 8.3 (High).

Operationally, ranked at the 28th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

OWASP Top 10 for Web (2025)

EU & UK References

Vulnerability Data

A CWE-287: Improper Authentication vulnerability exists that could allow a device to be compromised when a key of less than seven digits is entered and the attacker has access to the KNX installation.

CWE(s)

Related Threats

CVEs Like This One

CVE-2023-37196Same vendor: Schneider-Electric
CVE-2023-1049Same vendor: Schneider-Electric
CVE-2026-6866Same vendor: Schneider-Electric
CVE-2026-8045Same vendor: Schneider-Electric
CVE-2025-13844Same vendor: Schneider-Electric
CVE-2024-5559Same vendor: Schneider-Electric
CVE-2023-25555Same vendor: Schneider-Electric
CVE-2023-25620Same vendor: Schneider-Electric
CVE-2023-25619Same vendor: Schneider-Electric
CVE-2023-5629Same vendor: Schneider-Electric

Affected Assets

schneider-electric
merten instabus tastermodul 1fach system m firmware
1.0
schneider-electric
merten instabus tastermodul 2fach system m firmware
1.0
schneider-electric
merten tasterschnittstelle 4fach plus firmware
1.0, 1.2
schneider-electric
merten knx argus 180\/2\,20m up system firmware
1.0
schneider-electric
merten jalousie-\/schaltaktor reg-k\/8x\/16x\/10 m. hb firmware
1.0
schneider-electric
merten knx uni-dimmaktor ll reg-k\/2x230\/300 w firmware
1.0, 1.1
schneider-electric
merten knx schaltakt.2x6a up m.2 eing. firmware
0.1

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-287

Detects unauthorized successful logons resulting from improper authentication implementations.

addresses: CWE-287

Documented procedures ensure personnel are trained on authentication mechanisms, tangibly lowering the risk of improper authentication being exploited.

addresses: CWE-287

Security awareness training instructs users on secure authentication practices and avoiding credential compromise.

addresses: CWE-287

Training on authentication mechanisms and best practices decreases the occurrence of improper authentication.

addresses: CWE-287

Non-repudiation requires strong authentication mechanisms to irrefutably attribute performed actions to specific individuals or processes.

addresses: CWE-287

Session content review can reveal authentication bypasses or failures in session establishment.

addresses: CWE-287

Review of authentication-related audit records can detect improper authentication mechanisms or bypasses.

addresses: CWE-287

Assessments check authentication mechanisms for correct implementation and effectiveness, reducing successful authentication bypass attempts.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

blocks

Mandating segregated approval and oversight for non-human identities reduces the chance that weak or orphaned credentials can be exploited for unauthorized authentication.

blocks

A.5.17 directly mandates generation of non-guessable unique secrets, secure transmission, immediate change of defaults/temporary creds, strong password enforcement, no-reuse, and compromise response, which stops most improper-authentication exploits at source; the bounded remainder is non-password authentication methods and sufficiency-of-proof cases (e.g. IA-2/IA-5 enhancements) left to other controls.

blocks

Security requirements specified early and verified through testing drive the consistent implementation of authentication mechanisms, decreasing the likelihood that authentication steps are omitted or incorrectly applied.

blocks

A.8.26 explicitly requires identifying and addressing authentication-related requirements (including level of trust in identity via 8.5 and 5.17) as part of application development or acquisition, which prevents a slice of CWE-287 but leaves the dominant sufficiency-of-proof aspects (IA-2/IA-5) and many implementation defects untouched.

blocks

A.8.27 mandates security-by-design principles (least privilege, default-deny, never-trust/always-verify, MFA, end-to-end encryption of requests, distrust-external-input, secure session control, and explicit authentication/authorization in every layer), which directly stops most improper-authentication flaws from being exploitable; the bounded remainder is insufficient-proof cases that live only in the strength or correctness of the credential itself (IA-5/IA-2 territory).

blocks

A.8.5 directly mandates appropriate-strength authentication techniques, MFA for critical systems, protected log-on procedures, brute-force resistance, no cleartext passwords/transmission, and session controls that stop exploitation of insufficient proof of identity; the bounded remainder is cases where the chosen technique itself is flawed or insufficiently implemented (e.g. weak biometrics without fallback).

Hardening callouts derived

DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.

  • No fine-grained STIG row for CWE-287, a class-level weakness. Rules are authored against its narrower children: CWE-295, CWE-306.

References