CVE-2021-31924
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.
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
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 Medium
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - CVSS 2.0
- 4.6 Medium
AV: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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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 Medium
CVSS: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
| Package | Affected | Fixed |
|---|---|---|
pam-u2fAlpine:v3.15 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.16 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.17 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.18 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.19 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.20 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.21 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.22 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.23 |
before 1.1.1-r0 | 1.1.1-r0 |
pam-u2fAlpine:v3.24 |
before 1.1.1-r0 | 1.1.1-r0 |
History
| Recorded | Changed | Sources |
|---|---|---|
| affected, facts | ||
| affected, aliases, references | OSV | |
| affected | ||
| aliases | EUVD | |
| first indexed | CVE 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
yubico.com/support/security-advisories/ysa-2021-03
developers.yubico.com/pam-u2f
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CRBVOZEMVO72FV4Z5O4GBGSURXHWRGD3
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IL3I5AKECLMK4ADLLACLOEF7H5CMNDP2
security.gentoo.org/glsa/202208-11
nvd.nist.gov/vuln/detail/CVE-2021-31924
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lists.fedoraproject.org/archives/list/[email protected]/message/CRBVOZEMVO72FV4Z5O4GBGSURXHWRGD3
lists.fedoraproject.org/archives/list/[email protected]/message/IL3I5AKECLMK4ADLLACLOEF7H5CMNDP2
github.com/advisories/GHSA-v2qj-ch59-r5g4
security.alpinelinux.org/vuln/CVE-2021-31924
security-tracker.debian.org/tracker/CVE-2021-31924
ubuntu.com/security/CVE-2021-31924
cve.org/CVERecord?id=CVE-2021-31924
suse.com/security/cve/CVE-2019-12209
suse.com/security/cve/CVE-2019-12210
suse.com/security/cve/CVE-2021-31924