Elasticsearch is a popular open-source distributed search and analytics engine. It’s used by thousands of organizations for storing and quickly searching large amounts of data. However, in June 2025, a new security vulnerability was identified and assigned CVE-2025-37727. This vulnerability affects Elasticsearch instances configured for request auditing, particularly when using the Reindex API.

If misconfigured, this flaw can unintentionally leak sensitive data to log files, exposing secrets such as credentials or personal data—compromising your application confidentiality. In this long read, I’ll break down what CVE-2025-37727 is, show you where it happens (with example code), give you links to further references, and explain how attackers might exploit it.

What is CVE-2025-37727?

CVE-2025-37727 is a vulnerability found in some Elasticsearch versions where sensitive information sent through the _Reindex API_ is logged in plain text when request auditing is enabled.

Normally, log files should never contain secrets. But due to the way Elasticsearch logs incoming reindex requests (especially those using remote sources with embedded credentials), these secrets can accidentally end up written to disk.

You are vulnerable if

- You use the Reindex API with remote sources (copying data between clusters or pulling from a private HTTP endpoint).

If all three are true, any credentials in your reindex request may be written to the audit log.

Example: Where Sensitive Data Leaks

Imagine a DevOps user triggers a Reindex action to copy data from a protected remote Elasticsearch cluster. They use the Reindex API to specify the source credentials:

POST _reindex
{
  "source": {
    "remote": {
      "host": "https://private-cluster.example.com";,
      "username": "admin",
      "password": "mySuperSecretPwd"
    },
    "index": "secrets-backup"
  },
  "dest": {
    "index": "secrets-restored"
  }
}

If request auditing is enabled (xpack.security.audit.enabled: true), Elasticsearch logs the whole request body, including "username": "admin" and "password": "mySuperSecretPwd", straight into the audit log file!

A typical audit log entry might look like

{
  "event.type": "access_granted",
  ...
  "request.body": "{\"source\":{\"remote\":{\"host\":\"https://private-cluster.example.com\",\"username\":\"admin\",\"password\":\"mySuperSecretPwd\";}, ...}"
}

Now, anyone with access to the log file can see those credentials. This risk is bigger if logs are shipped off-host or shared with third parties.

Exploit Details

While this vulnerability doesn't allow direct remote exploitation (it doesn't grant control over Elasticsearch), it enables lateral movement or privilege escalation by any insider or attacker who can read the audit logs.

Responsible Logging: Mitigation Steps

- Do NOT pass secrets in API calls: Use secure settings for remote API credentials instead of putting them in the request body.
- Upgrade to patched Elasticsearch versions: The Elastic team is expected to release patches sanitizing logs by default (removing or masking sensitive fields).
- Rotate secrets: If you used the Reindex API with embedded credentials and had audit logging enabled, rotate those passwords immediately.

Further Reading

- Official Documentation of Elasticsearch Reindex API
- Elastic Security & Audit Logging Guide
- National Vulnerability Database: CVE-2025-37727

Summary

CVE-2025-37727 is a serious confidentiality issue for Elasticsearch admins using both remote Reindex API and audit logging. Always treat log files as sensitive, and never include secrets in your API payloads—especially when using features like audit logging. Patch your clusters and clean up old logs to stay safe.

If you’re reading this, audit your log practices and double-check for secrets in your logs—before someone less friendly does!


Stay tuned for updates from Elastic and secure your deployments today.

Timeline

Published on: 10/10/2025 10:15:34 UTC
Last modified on: 10/14/2025 19:37:28 UTC