CVE-2026-4633Network attack vector

User enumeration via differential login errors

Published Mar 23, 2026 · Updated Mar 23, 2026

Information disclosure in Red Hat build of Keycloak allows remote attackers to enumerate users through identity-first login errors. AbstractUsernameFormAuthenticator.getDefaultChallengeMessage returns a password-only error after resolving a username, distinguishing existing accounts from invalid usernames. Exploitation requires Organizations and the identity-first login flow to be enabled; the flaw reveals account existence but does not alter data or service availability.

CVSS severity3.7
Low
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Red Hat build of Keycloak allows remote attackers to enumerate users through identity-first login errors. AbstractUsernameFormAuthenticator.getDefaultChallengeMessage returns a password-only error after resolving a username, distinguishing existing accounts from invalid usernames. Exploitation requires Organizations and the identity-first login flow to be enabled; the flaw reveals account existence but does not alter data or service availability.

The record

CVE
CVE-2026-4633
Published
Mar 23, 2026
Updated
Mar 23, 2026
Vendor
389 Directory Server
Product
Red Hat build of Keycloak
Classifications
CWE-209, T1589.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 23, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 23, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

389 Directory Server · Red Hat build of KeycloakAffected versions are unavailable in this record.

Published CVSS scores

3.7NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
3.7Red HatCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-209Generation of Error Message Containing Sensitive Information
T1589.003Gather Victim Identity Information: Employee Names

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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