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CVE-2021-31924

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and...

6.8 MediumFix available

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Attack profile

How easy it is to exploit

Attack vector
Physical
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

0.33%Down 0.3 points since May 26, 2021
90%50%10%1%

What each source reports

NVD Score used 6.8

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
CVE-2021-31924
CVSS 3.1
6.8 MediumCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 2.0
4.6 MediumAV:L/AC:L/Au:N/C:P/I:P/A:P
Weakness
CWE-287
Updated
2026-11-02
CVE List No score

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
CVE-2021-31924
Updated
2026-11-02
EUVDEUVD-2021-18797 No score

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
EUVD-2021-18797
Updated
2026-11-03
GitHub AdvisoriesGHSA-v2qj-ch59-r5g4 6.8

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and...

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
GHSA-v2qj-ch59-r5g4
CVSS 3.1
6.8 MediumCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-287
Updated
2026-11-02
OSVALPINE-CVE-2021-31924 6.8

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
ALPINE-CVE-2021-31924
CVSS 3.1
6.8 MediumCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-03
OSV 6.8

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
CVE-2021-31924
CVSS 3.1
6.8 MediumCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2021-31924 6.8

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
DEBIAN-CVE-2021-31924
CVSS 3.1
6.8 MediumCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2021-31924 6.8

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

Record
UBUNTU-CVE-2021-31924
CVSS 3.1
6.8 MediumCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVopenSUSE-SU-2024:11145-1 No score

pam_u2f-1.1.1-1.3 on GA media

These are all security issues fixed in the pam_u2f-1.1.1-1.3 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:11145-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
pam-u2f
Alpine:v3.15
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.16
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.17
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.18
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.19
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.20
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.21
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.22
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.23
before 1.1.1-r0
1.1.1-r0
pam-u2f
Alpine:v3.24
before 1.1.1-r0
1.1.1-r0
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Affected packages
PackageAffectedFixed
pam-u2f
Debian:12
before 1.1.0-1.1
1.1.0-1.1
pam-u2f
Debian:13
before 1.1.0-1.1
1.1.0-1.1
pam-u2f
Debian:14
before 1.1.0-1.1
1.1.0-1.1
pam_u2f
openSUSE:Tumbleweed
From an advisory covering 3 CVEs
before 1.1.1-1.3
1.1.1-1.3

History

History
RecordedChangedSources
affected, facts
affected, aliases, referencesOSV
affected
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-31924 is a medium vulnerability (CVSS 6.8) in Yubico Pam-u2f, published May 25, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.33%, the 26th percentile. Fixed in pam-u2f 1.1.1-r0.

References

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