CVE-2021-43177Network attack vector

Account access via trailing-interval TOTP reuse

Published Apr 11, 2022 · Updated Aug 4, 2024

Improper OTP validation in Devise-Two-Factor before 4.0.2 allows remote authenticated users to reuse a consumed TOTP. The validate_and_consume_otp! path rejects replay only during the current 30-second interval, so the code becomes valid again while allowed drift remains. Exploitation requires account credentials and a recently consumed or captured TOTP, then grants access as that account during the immediately trailing interval.

CVSS severity5.3
Medium
EPSS probability0.88%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper OTP validation in Devise-Two-Factor before 4.0.2 allows remote authenticated users to reuse a consumed TOTP. The validate_and_consume_otp! path rejects replay only during the current 30-second interval, so the code becomes valid again while allowed drift remains. Exploitation requires account credentials and a recently consumed or captured TOTP, then grants access as that account during the immediately trailing interval.

The record

CVE
CVE-2021-43177
Published
Apr 11, 2022
Updated
Aug 4, 2024
Vendor
Devise-Two-Factor
Product
Devise-Two-Factor
Classifications
CWE-254, T1078
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 11, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Devise-Two-Factor · Devise-Two-Factorversion=< 4.0.2

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
3.5NIST NVDAV:N/AC:M/Au:S/C:P/I:N/A:N
5.3GitHubCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-2547PK - Security Features
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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