Cyber Resilience

CVE-2023-20123

Auth Bypass in Cisco Duo ≤ 2.0.1

Auth Bypass
Published
05 April 2023
Modified
21 November 2024
Patch / advisory
View advisory
CVSS Score v3.1 6.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:P/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS Score 0.0025 16th percentile
Risk Priority 45 floored blend · peak EPSS

Summary

CVE-2023-20123 is a medium-severity Authentication Bypass by Capture-replay (CWE-294) vulnerability in Cisco Duo. Its CVSS base score is 6.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Network Sniffing (T1040); ranked at the 16th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

A vulnerability in the offline access mode of Cisco Duo Two-Factor Authentication for macOS and Duo Authentication for Windows Logon and RDP could allow an unauthenticated, physical attacker to replay valid user session credentials and gain unauthorized access to an…

more

affected macOS or Windows device. This vulnerability exists because session credentials do not properly expire. An attacker could exploit this vulnerability by replaying previously used multifactor authentication (MFA) codes to bypass MFA protection. A successful exploit could allow the attacker to gain unauthorized access to the affected device.

CWE(s)
CWE-294

Related Threats

MITRE ATT&CK Enterprise Techniques

T1040 Network Sniffing Credential Access
Adversaries may passively sniff network traffic to capture information about an environment, including authentication material passed over the network.
attack.mitre.org →
T1550.003 Pass the Ticket Lateral Movement
Adversaries may “pass the ticket” using stolen Kerberos tickets to move laterally within an environment, bypassing normal system access controls.
attack.mitre.org →
T1550.004 Web Session Cookie Lateral Movement
Adversaries can use stolen session cookies to authenticate to web applications and services.
attack.mitre.org →
T1557 Adversary-in-the-Middle Credential Access
Adversaries may attempt to position themselves between two or more networked devices using an adversary-in-the-middle (AiTM) technique to support follow-on behaviors such as [Network Sniffing](https://attack.
attack.mitre.org →
T1021 Remote Services Lateral Movement
Adversaries may use [Valid Accounts](https://attack.
attack.mitre.org →
T1021.002 SMB/Windows Admin Shares Lateral Movement
Adversaries may use [Valid Accounts](https://attack.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-20301Same product: Cisco Duo Authentication For Windows Logon And Rdp
CVE-2023-20199Same product: Cisco Duo
CVE-2024-20292Same product: Cisco Duo Authentication For Windows Logon And Rdp
CVE-2025-20258Same product: Cisco Duo
CVE-2024-38284Shared CWE-294
CVE-2025-67135Shared CWE-294
CVE-2025-8616Shared CWE-294
CVE-2023-6374Shared CWE-294
CVE-2026-57574Shared CWE-294
CVE-2023-33854Shared CWE-294

Affected Assets

cisco
duo
≤ 2.0.1
cisco
duo authentication for windows logon and rdp
≤ 4.2.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V10.4.16
  • V10.5.1

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.

AC-9 Previous Logon Notification
addresses: CWE-294

Allows detection of capture-replay attacks by showing the replayed logon's timestamp as the last logon.

SC-23 Session Authenticity
addresses: CWE-294

Protects against replay of captured session tokens or credentials by requiring authenticated, fresh session channels.

SC-40 Wireless Link Protection
addresses: CWE-294

Wireless link protections commonly incorporate replay protection, reducing the exploitability of capture-replay weaknesses.

SC-45 System Time Synchronization
addresses: CWE-294

Accurate synchronized time enables tight timestamp windows that directly limit capture-replay windows in authentication protocols.

Mitigating Controls (NIST CSF 2.0) AI

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

PR.AA-04 mostly match
prevents

Protecting and verifying identity assertions prevents replay of captured authentication material.

PR.DS-02 mostly match
prevents

Encryption and integrity protections for data-in-transit directly block capture-replay of credentials or tokens.

DE.CM-01 partial match
prevents

Network monitoring may detect anomalous replays after the fact but does not prevent the design flaw.

PR.AA-03 partial match
prevents

Strong authentication methods can reduce replay risk but do not inherently address captured messages.

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.

A.8.24 Use of cryptography mostly match
prevents

Cryptographic protections (e.g., nonces, timestamps, message authentication codes) make captured authentication messages unusable for replay.

A.8.5 Secure authentication mostly match
prevents

Secure authentication mechanisms directly prevent replay attacks by requiring fresh, non-replayable credentials or tokens.

A.8.20 Networks security partial match
mitigates

Network security controls such as encryption and integrity protection reduce the feasibility of capturing and replaying authentication traffic.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate replay-resistant authentication designs, but the control itself does not prescribe the technical measures.

References