CVE-2021-3754
Keycloak's improper input validation allows using email as username
A flaw was found in keycloak where an attacker is able to register himself with the username same as the email ID of any existing user. This may cause trouble in getting password recovery email in case the user forgets the password.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
Exploit likelihood
What each source reports
NVD Score used
A flaw was found in keycloak where an attacker is able to register himself with the username same as the email ID of any existing user. This may cause trouble in getting password recovery email in case the user forgets the password.
- Record
CVE-2021-3754- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-20
- Updated
- 2026-11-02
CVE List No score
A flaw was found in keycloak where an attacker is able to register himself with the username same as the email ID of any existing user. This may cause trouble in getting password recovery email in case the user forgets the password.
- Record
CVE-2021-3754- Weakness
- CWE-20
- Updated
- 2026-11-02
EUVDEUVD-2024-1917 No score
A flaw was found in keycloak where an attacker is able to register himself with the username same as the email ID of any existing user. This may cause trouble in getting password recovery email in case the user forgets the password.
- Record
EUVD-2024-1917- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-4vc8-pg5c-vg4x
Keycloak's improper input validation allows using email as username
Keycloak allows the use of email as a username and doesn't check that an account with this email already exists. That could lead to the unability to reset/login with email for the user. This is caused by usernames being evaluated before emails.
- Record
GHSA-4vc8-pg5c-vg4x- CVSS 3.1
- 3.7 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-670
- Updated
- 2026-11-02
OSV
A flaw was found in keycloak where an attacker is able to register himself with the username same as the email ID of any existing user. This may cause trouble in getting password recovery email in case the user forgets the password.
- Record
CVE-2021-3754- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Updated
- 2026-11-02
OSVGHSA-4vc8-pg5c-vg4x
Keycloak's improper input validation allows using email as username
Keycloak allows the use of email as a username and doesn't check that an account with this email already exists. That could lead to the unability to reset/login with email for the user. This is caused by usernames being evaluated before emails.
- Record
GHSA-4vc8-pg5c-vg4x- CVSS 3.1
- 3.7 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L - Weakness
- CWE-670
- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
org.keycloak:keycloak-servicesMaven |
before 24.0.1 | 24.0.1 |
org.keycloak:keycloak-servicesMaven |
before 24.0.1, plus listed versions 1.0-alpha-11.0-alpha-1-120620131.0-alpha-21.0-alpha-31.0-alpha-4 Show 45 moreShow less1.0-beta-11.0-beta-1-201505211.0-beta-1-201505231.0-beta-21.0-beta-31.0-beta-41.0-final1.0-rc-11.0-rc-21.0.1.Final1.0.2.Final1.0.3.Final1.0.4.Final1.0.5.Final1.1.0.Beta11.1.0.Beta21.1.0.Final1.1.1.Final1.2.0.Beta11.2.0.CR11.2.0.Final1.3.0.Final1.3.1.Final1.4.0.Final1.5.0-Final1.5.0.Final1.5.1.Final1.6.0.Final1.6.1.Final1.7.0.CR11.7.0.Final1.8.0.Alpha11.8.0.CR11.8.0.CR21.8.0.CR31.8.0.Final1.8.1.Final1.9.0.CR11.9.0.Final1.9.1.Final1.9.2.Final1.9.3.Final1.9.4.Final1.9.5.Final1.9.7.Final |
24.0.1 |
Public exploits
Links only. Every CVE stores no exploit code.
| Source | Link | Date |
|---|---|---|
| PoC in GitHub | 7Ragnarok7/CVE-2021-3754 | 2023-09-07 |
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases, products | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV, PoC in GitHub |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-3754 is a medium vulnerability (CVSS 5.3) in Keycloak, published August 26, 2022. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 2.19%, the 82nd percentile. Fixed in org.keycloak:keycloak-services 24.0.1.
References
bugzilla.redhat.com/show_bug.cgi?id=1999196
access.redhat.com/security/cve/CVE-2021-3754
github.com/keycloak/keycloak/security/advisories/GHSA-4vc8-pg5c-vg4x
nvd.nist.gov/vuln/detail/CVE-2021-3754
Left out here: 119 versions. The JSON record has them.