CVE-2023-20859 - Sensitive Information Leakage in Spring Vault Through Log Files

When it comes to protecting sensitive data, secrets management tools like Spring Vault are a major asset for modern applications. However, sometimes security flaws crop up in the very tools we depend on. Enter CVE-2023-20859, a vulnerability discovered in Spring Vault that can leak secrets in a place you’d least expect: your log files.

In this post, we’ll break down what this vulnerability is, how it affects applications using Spring Vault (including a code example), and share resources for learning more. We’ll keep the language clear and use concrete examples so you can understand the risk — and, most importantly, protect your data.

What is CVE-2023-20859?

Spring Vault is a Java library that lets applications talk to HashiCorp Vault, a popular secrets manager. The vulnerability with ID CVE-2023-20859 affects:

And all older, unsupported versions.

The issue? When an app tries to revoke a Vault batch token and an error happens, sensitive token information may get written to the application log.

The Risk: Sensitive Log Exposure

If you’re using batch tokens to control Vault access, and a revoke operation fails (for example, due to network or permission problems), your token may be printed in the application log. Attackers, or even just curious insiders, can read the logs, copy the token, and (if still valid) use it to grab secrets from Vault.

Vulnerable Code in the Wild

Let’s see how this can happen with Spring Vault. Here’s a sample snippet that interacts with Vault tokens:

import org.springframework.vault.core.VaultTemplate;
import org.springframework.vault.support.VaultToken;

public class VaultTokenRevoker {

    private final VaultTemplate vaultTemplate;

    public VaultTokenRevoker(VaultTemplate vaultTemplate) {
        this.vaultTemplate = vaultTemplate;
    }

    public void revokeToken(VaultToken token) {
        try {
            vaultTemplate.opsForToken().revoke(token);
        } catch (Exception ex) {
            // Logging the exception, which might include sensitive token information
            System.err.println("Failed to revoke token: " + ex.getMessage());
        }
    }
}

If revoke(token) fails, the error goes to the logs.

- Prior to Spring Vault 3..2 and 2.3.3, the exception message could contain the full token value in plaintext.

Suppose you run your Java application and revoke a batch token

VaultToken token = VaultToken.of("s.GP3znQ3nV99qjJzioswCjsXv"); // This is your sensitive Vault token!
new VaultTokenRevoker(vaultTemplate).revokeToken(token);

If Vault is unreachable or you have permission issues, the log might catch something like

Failed to revoke token: 403 Forbidden @ POST /v1/auth/token/revoke (token: s.GP3znQ3nV99qjJzioswCjsXv)

Now imagine your logs are being shipped to a central system, or engineers/attackers are poking around. They have full access to a token that may allow reading or even writing secrets from Vault.

How Do I Fix or Mitigate This?

Upgrade, upgrade, upgrade!

Spring Vault 2.3.3 or later

As noted in the official advisory and the Spring security report, these versions sanitize exception messages to make sure sensitive tokens don’t leak into logs.

Avoid logging exception messages directly from failed Vault operations.

- Filter logs that mention revoke or /v1/auth/token/revoke.

Key Takeaways

- Never trust your logs: Always assume logs may become public someday. Don’t let them contain secrets!

Patch dependencies ASAP: Even small library updates can fix critical security bugs.

- Audit and rotate: After fixing, scan your logs for leaked tokens and rotate any that may have been exposed.

References & Further Reading

- Spring Security Advisory CVE-2023-20859
- VMware Tanzu Security CVE-2023-20859
- GitHub Commit Fix for CVE-2023-20859
- HashiCorp Vault Documentation

Final Thoughts

Vulnerabilities like CVE-2023-20859 remind us of the hidden dangers in software we rely on every day. If you use Spring Vault, double-check your version, patch if needed, and audit your logs for leaks. Keeping secrets… secret… demands constant vigilance.

Stay safe, patch often, and always treat your logs as potential windows into your most guarded secrets!

Timeline

Published on: 03/23/2023 21:15:00 UTC
Last modified on: 03/28/2023 13:46:00 UTC