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MEDIUM severity

CVE-2021-3754 — keycloak-services

MEDIUMFix: keycloak/keycloak@f970803

CVE-2021-3754 is a medium-severity (CVSS 5.3) Improper Input Validation vulnerability in org.keycloak:keycloak-services. A fix is available for org.keycloak:keycloak-services — see the affected versions and patch details below.

Keycloak's improper input validation allows using email as username

Also known asGHSA-4vc8-pg5c-vg4x
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 31, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.2%probability of exploitation in next 30 days
Lower Risk+0.05%
Lower risk than most CVEs82th percentile — riskier than 82% of all scored CVEsHighest risk
0.00%5.15%10.3%15.5%12.3%2.2%May 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
☕org.keycloak:keycloak-services

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.keycloak:keycloak-servicesall versions24.0.1org.keycloak:keycloak-services:24.0.1

Affected Products

2 products · 2 configurations
Application
keycloakredhat
all
Application
single sign-onredhat
1 version
7.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.keycloak:keycloak-services, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.keycloak:keycloak-services to 24.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3754 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow
Workaround published by Red Hat
The workaround is to enable "Email as username" flag or disable "Login with email" in the login settings
Source: Red Hat security advisory for CVE-2021-3754 (CC BY 4.0)

Frequently Asked Questions

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.
O3 Security · Impact-Aware SCA

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CVE-2021-3754: keycloak-services — Fixed in 24.0.1