CVE-2021-36749: Apache Druid HTTP InputSource authorization bypass allows local file read

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 18 September 2026. Confidence: high.

high priorityThe flaw gives authenticated local file read with high confidentiality impact and a very high EPSS score, though it requires valid credentials and is not known to be exploited in the wild.

What it is

Apache Druid's HTTP InputSource lets an authenticated user supply a file URL and read data from sources other than intended, including the local file system, with the privileges of the Druid server process. It matters most when Druid sits behind an application that permits the HTTP InputSource but blocks the Local InputSource, because the application-level restriction can be bypassed. The fix claimed for 0.21.0 under CVE-2021-26920 was not actually present in 0.21.0 or 0.21.1.

Impact

An attacker with a Druid account gains read access to files reachable by the Druid server process, exposing configuration, credentials or other sensitive local data. The CVSS vector rates confidentiality impact as high with no integrity or availability effect.

Attack surface

Reached over the network through the Druid ingestion interface by an authenticated user; no user interaction is required. The flaw is an incorrect authorization check (CWE-863) on the HTTP InputSource, and the practical risk is highest where Druid is accessed indirectly through a front-end application.

Exploitation

Not listed in CISA KEV and no ransomware usage is documented, but EPSS is very high at 0.809 (99.6th percentile), indicating substantial predicted exploitation activity. References are vendor advisories and mailing list posts only, with no public exploit tag.

What to do

• Upgrade Apache Druid past the affected 0.21.0 and 0.21.1 releases to a version where the HTTP InputSource restriction is actually enforced.
• If upgrade is not immediate, restrict or disable the HTTP InputSource for untrusted users and block ingestion configurations that accept arbitrary file URLs.
• Ensure Druid is never exposed directly to untrusted networks and that front-end applications cannot pass user-controlled URLs into the HTTP InputSource.
• Run the Druid server process with a least-privilege account and limit its read access to sensitive local files and directories.
• Audit Druid accounts and ingestion permissions, removing or narrowing access for users who do not need to define input sources.

Detection

• Monitor Druid ingestion requests and task logs for HTTP InputSource configurations containing file:// or other local path URLs.
• Alert on Druid server process reads of sensitive files such as /etc/passwd, configuration files or credential stores.
• Review Druid audit and access logs for ingestion task creation by accounts that normally do not submit ingestion jobs.
• Correlate outbound or local file access by the Druid process with ingestion task activity to spot unauthorized data reads.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.