CVE-2023-6484 - Log Injection Vulnerability in Keycloak WebAuthn Explained (with Code Example & Exploit Details)

Keycloak is an open-source software solution for identity and access management, used worldwide to secure web apps and services. In January 2024, a new flaw—log injection (CVE-2023-6484)—was discovered in Keycloak’s WebAuthn authentication form that could mess with logs' accuracy. This vulnerability slipped through unnoticed until recently, and while its impact is minor, it’s crucial for anyone running Keycloak to understand what happened and why it matters.

In this post, I’ll walk you through CVE-2023-6484 in simple language, show how it can be exploited with a code example, and summarize best practices for protecting your systems.

What is CVE-2023-6484?

CVE-2023-6484 is a log injection flaw found in Keycloak’s WebAuthn authentication. Log injection (sometimes called log forging) happens when a vulnerable app lets users inject special characters like \n (newline) into log entries, allowing them to manipulate the format or content of log files. Attackers might use this to confuse log analysis tools, hide actions, or poison logs with misleading entries.

In Keycloak, when using *WebAuthn* (the browser-based standard for passwordless logins), user input taken from the authentication form wasn’t properly sanitized before adding to server logs. As a result, attackers could insert custom log lines by entering crafted strings at the login screen.

Original References & Disclosure

- Red Hat Security Advisory
- Keycloak Issue Tracker (KEYCLOAK-23272)
- NVD Entry for CVE-2023-6484

Example Exploit Scenario

Suppose you control a browser and are logging into a Keycloak instance using WebAuthn. In the WebAuthn form, for the "username" field, you could enter something like:

Alice\n[INFO] User admin granted SUPER_ADMIN by attacker

This payload includes \n, which is interpreted as a new line.

Keycloak code before the patch might log it like this

LOGGER.info("User " + username + " attempted WebAuthn login");

If you enter the malicious value above, logs would look like this

2024-06-04 14:23:45 INFO  User Alice
[INFO] User admin granted SUPER_ADMIN by attacker attempted WebAuthn login

*Notice the log appears as if 'admin' received privileges, and the real login action is hidden!*

Minimal Proof-of-Concept in Python

To demonstrate what’s going on behind the scenes, here’s a minimal simulation in Python. This isn’t actual Keycloak code, but it shows how unfiltered input can alter logs.

def log_login(username):
    print(f"User {username} attempted WebAuthn login")

# Malicious payload
malicious_username = "Alice\n[INFO] User admin granted SUPER_ADMIN by attacker"
log_login(malicious_username)

Output

User Alice
[INFO] User admin granted SUPER_ADMIN by attacker attempted WebAuthn login

If a system later parses logs to audit actions, this fake line could cause confusion or hide real events.

Impact

- Severity: Low/minor (can't directly compromise the server, but can disrupt log forensics)

Hide malicious logins or operations

- Trick SIEM/log monitoring

Frustrate incident responders

This vulnerability does not grant direct access, privilege escalation, or remote control. It’s a tool for deception in combination with other attacks.

Fix (in Simple Terms)

The fix, pushed in this commit, is straightforward: sanitize user input before writing it to logs.

Here’s pseudocode showing how to patch this

// Before
LOGGER.info("User " + username + " attempted WebAuthn login");

// After: escape newlines
LOGGER.info("User " + escapeForLogs(username) + " attempted WebAuthn login");

String escapeForLogs(String input) {
    return input.replaceAll("[\r\n]", "_");
}

Now, the injected strings can’t break log formatting.

Preventing Log Injection: Best Practices

1. Always sanitize user input before writing to logs. Replace or remove control/newline characters.

Limit the details logged to only necessary information.

3. Monitor for suspicious log entries, such as those starting with unexpected prefixes or extra lines.

Conclusion

While CVE-2023-6484 isn’t a headline-grabbing critical flaw, it’s a smart reminder why *every* user input—no matter how “safe” it appears—deserves scrutiny. Log injection can complicate investigations and add noise for security teams. Patching Keycloak and reviewing your logging hygiene today will help you avoid bigger headaches later.

Timeline

Published on: 04/25/2024 16:15:09 UTC
Last modified on: 06/12/2024 10:09:42 UTC