CVE-2021-43177

As a result of an incomplete fix for CVE-2015-7225, in versions of devise-two-factor prior to 4.0.2 it is possible to reuse a One-Time-Password (OTP) for one (and only one) immediately trailing interval. CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N)

Published: 2022-04-11 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-43177 is rated Moderate Risk (42/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.39%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-43177

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-01-14 0.29% 0.39% +0.09%
2 2025-11-10 0.39% 0.29% -0.09%
3 2025-11-09 — 0.39% —

Full EPSS history (11 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-43177

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 1.6 3.6 [email protected]
3.5 2.0 LOW
AV:N/AC:M/Au:S/C:P/I:N/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:S)
A single authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 6.8 2.9 [email protected]

Weakness enumeration for CVE-2021-43177

GitHub Security Advisory for CVE-2021-43177

GHSA-jm35-h8q2-73mp · Severity: medium · Ecosystem: rubygems — Improper one time password handling in devise-two-factor

OS Trackers for CVE-2021-43177

vendor priority summary link
debian not yet assigned CVE-2021-43177 not yet assigned priority: Debian including 1 source packages (ruby-devise-two-factor), 2 status rows across 2 suites (bookworm, bullseye): open 1, resolved 1. https://security-tracker.debian.org/tracker/CVE-2021-43177
ubuntu medium CVE-2021-43177 medium priority: Ubuntu including 1 source packages (ruby-devise-two-factor), 14 status rows across 14 suites (bionic, focal, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 5, DNE 3, released 3, ignored 2, needed 1. https://ubuntu.com/security/CVE-2021-43177

Affected software / configurations for CVE-2021-43177

Vendor Product Version Raw CPE
tinfoilsecurity devise-two-factor < 4.0.2 cpe:2.3:a:tinfoilsecurity:devise-two-factor:*:*:*:*:*:*:*:*

References for CVE-2021-43177

cvelogic Threat Intelligence