CVE-2025-8419: Red Hat Keycloak SMTP Injection Vulnerability

CVE-2025-8419 Overview

CVE-2025-8419 affects Red Hat Keycloak, an open source identity and access management solution. The flaw resides in the e-mail registration workflow, where special characters supplied by an attacker are not properly sanitized before being passed to the Simple Mail Transfer Protocol (SMTP) layer. An unauthenticated attacker can leverage this weakness to inject SMTP commands and cause the Keycloak server to send short, attacker-influenced e-mails. The local part of the e-mail address is capped at 64 characters, so injected payloads are constrained to brief subjects and minimal body content. The issue is tracked as [CWE-93] Improper Neutralization of CRLF Sequences.

Critical Impact
Unauthenticated remote attackers can coerce a Keycloak server into sending unsolicited e-mails, which may serve as a precursor to phishing or social engineering campaigns leveraging the trusted Keycloak sender identity.

Affected Products

Red Hat Keycloak (keycloak-services component)
Red Hat build of Keycloak distributions covered by RHSA-2025:15336, RHSA-2025:15337, RHSA-2025:15338, and RHSA-2025:15339
Deployments using Keycloak self-registration with SMTP configured

Discovery Timeline

2025-08-06 - CVE-2025-8419 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-8419

Vulnerability Analysis

The vulnerability is an SMTP header injection issue in the Keycloak keycloak-services module. During self-registration, Keycloak accepts an e-mail address from the user and later uses that value when constructing outbound SMTP messages, for example to send a verification link. The local part of the address (before the @) is not sufficiently neutralized for control characters. An attacker can embed carriage-return and line-feed (CRLF) sequences plus additional SMTP header directives inside the e-mail field. When Keycloak passes the value to the mail transport, the injected sequences are interpreted as new header lines or body content by the SMTP client.

Because Keycloak enforces a 64-character limit on the local part, the injection payload is short. Attackers can still deliver a compact subject line and a small body, which is sufficient for phishing lures or link-bait content that abuses the trust of the Keycloak sender domain.

Root Cause

The root cause is missing neutralization of CRLF and other SMTP metacharacters in the registration e-mail field before it is used to compose outbound mail. The keycloak-services layer treats user-controlled input as trusted when building SMTP envelope and header data, allowing header injection as described in [CWE-93].

Attack Vector

Exploitation requires only network access to a Keycloak instance with self-registration and SMTP e-mail sending enabled. No authentication or user interaction is required. The attacker submits a crafted registration request containing an e-mail whose local part carries embedded CRLF sequences followed by additional SMTP header directives. Keycloak then generates and sends the resulting short e-mail, which appears to originate from the legitimate Keycloak sender.

No public proof-of-concept exploit is listed for CVE-2025-8419, and the issue is not present in the CISA Known Exploited Vulnerabilities catalog. Refer to the Red Hat CVE Details for CVE-2025-8419 and Red Hat Bugzilla Report #2385776 for vendor technical details.

Detection Methods for CVE-2025-8419

Indicators of Compromise

Registration requests containing e-mail values with encoded or literal CRLF (%0d%0a, \r\n) sequences in the local part
Outbound SMTP messages from the Keycloak server with unexpected subject lines or recipients that do not match legitimate verification flows
Spikes in registration attempts using unusual or malformed e-mail addresses under the 64-character local-part limit
User reports of unsolicited e-mails apparently originating from the Keycloak sender domain

Detection Strategies

Inspect Keycloak access logs and reverse proxy logs for registration endpoint requests containing control characters or URL-encoded newline sequences in e-mail parameters
Correlate Keycloak mail-send events with the corresponding registration events to identify e-mails that do not map to a legitimate new account
Alert on outbound SMTP traffic from the Keycloak host with header patterns that deviate from the standard verification template

Monitoring Recommendations

Enable verbose audit logging for the Keycloak registration flow and forward events to a centralized SIEM for pattern analysis
Monitor SMTP relay logs for message volume anomalies and non-standard header fields originating from Keycloak service accounts
Track failed and successful registrations by source IP to identify automated abuse of the registration endpoint

How to Mitigate CVE-2025-8419

Immediate Actions Required

Apply the Red Hat security updates referenced in RHSA-2025:15336, RHSA-2025:15337, RHSA-2025:15338, and RHSA-2025:15339 to all affected Keycloak deployments
If patching is not immediately possible, disable public self-registration on Keycloak realms that expose SMTP-backed verification flows
Restrict outbound SMTP traffic from Keycloak hosts to approved relays and recipient domains
Review recent registration and mail-send logs for evidence of injection attempts

Patch Information

Red Hat has released fixed builds of Keycloak. Refer to Red Hat Security Advisory RHSA-2025:15336, RHSA-2025:15337, RHSA-2025:15338, and RHSA-2025:15339 for package versions and deployment guidance. Additional details are available in the Red Hat CVE Details for CVE-2025-8419.

Workarounds

Disable user self-registration in Keycloak realm settings until patches are applied
Enforce stricter server-side validation of the e-mail field, rejecting any input containing \r, \n, or their encoded equivalents
Place a web application firewall (WAF) rule in front of the Keycloak registration endpoint to block requests containing CRLF sequences in e-mail parameters
Rotate any SMTP credentials used by Keycloak if injection activity is confirmed in logs

bash

# Configuration example: disable self-registration via kcadm
kcadm.sh update realms/<realm-name> \
  -s registrationAllowed=false \
  -s registrationEmailAsUsername=false