CVE-2025-66518: 
Java vulnerability analysis and mitigation

CVE-2025-66518 is a path traversal vulnerability in Apache Kyuubi Server that allows authenticated clients to bypass the server-side kyuubi.session.local.dir.allow.list configuration and access local files outside the permitted directories. It affects Apache Kyuubi versions 1.6.0 through 1.10.2 (Maven artifact org.apache.kyuubi:kyuubi-server_2.12). The vulnerability was reported by Hiroki Egawa, disclosed on January 5, 2026, and assigned a CVSS v3.1 base score of 8.8 (High) and a CVSS v4.0 base score of 8.8 (High) (Github Advisory, Openwall OSS-Sec).

The root cause is missing path normalization when processing file paths supplied by clients via Kyuubi frontend protocols (CWE-22: Path Traversal; CWE-27: Path Traversal using dir/../../filename sequences). The server fails to properly neutralize ../ sequences in client-supplied pathnames before checking them against the kyuubi.session.local.dir.allow.list allowlist, allowing an attacker to craft a path that resolves outside the restricted directories. Exploitation requires low-level authenticated access to the Kyuubi frontend (e.g., Thrift JDBC/ODBC interface) but no special administrative privileges (Github Advisory, Openwall OSS-Sec).

Successful exploitation allows an authenticated network client to read and potentially modify local files on the Kyuubi server host that are outside the configured allowlist, resulting in high confidentiality and integrity impact. In data lakehouse environments where Kyuubi acts as a multi-tenant SQL gateway, this could expose sensitive configuration files, credentials, or data assets stored on the server. Availability impact is rated low, and subsequent system impact (e.g., downstream data stores) is also rated high for confidentiality and integrity (Github Advisory, Feedly).

1. Gain authenticated access: Obtain valid credentials for the Apache Kyuubi Server and connect via a supported frontend protocol such as the Thrift JDBC/ODBC interface (e.g., using a Hive JDBC client or Beeline).
2. Identify the allowlist: Determine the configured kyuubi.session.local.dir.allow.list value (e.g., /data/allowed/) by reviewing server configuration or through trial and error.
3. Craft a path traversal payload: Construct a file path that starts within an allowed directory but uses ../ sequences to escape it, for example: /data/allowed/../../etc/passwd or /data/allowed/../../../sensitive/config.properties.
4. Submit the traversal path: Use a Kyuubi SQL command or session configuration that references local files (e.g., loading a local resource or setting a session-level local directory) with the crafted traversal path.
5. Access unauthorized files: The server, lacking proper path normalization before the allowlist check, resolves the traversal and grants access to the target file outside the permitted directory, enabling data exfiltration or modification (Openwall OSS-Sec, Github Advisory).

• Logs: Kyuubi server access logs showing session requests referencing file paths containing ../ or ..%2F sequences; log entries for file access to paths outside the configured kyuubi.session.local.dir.allow.list directories.
• File System: Unexpected access timestamps on sensitive server files (e.g., /etc/passwd, configuration files, credential stores) that do not correspond to normal administrative activity.
• Network: Unusual or high-frequency JDBC/ODBC connections from unfamiliar client IPs to the Kyuubi Thrift port (default: 10009); connections from clients not previously seen in normal operations.
• Process: Kyuubi server process reading files in directories not normally accessed during routine SQL operations.

Users should upgrade Apache Kyuubi to version 1.10.3 or later, which includes the fix for missing path normalization (Github Advisory, Openwall OSS-Sec). As interim mitigations, restrict access to Kyuubi frontend protocols to only trusted and known clients using network-level controls (firewalls, VPNs, or IP allowlists). Additionally, audit access logs for suspicious file path patterns and ensure the kyuubi.session.local.dir.allow.list is configured as restrictively as possible.

The vulnerability was disclosed via the Apache Security mailing list and oss-security by Akira Ajisaka on January 5, 2026, crediting Hiroki Egawa as both reporter and remediation developer (Openwall OSS-Sec). Security news outlets such as SecurityOnline.info covered the flaw, describing it as a high-severity issue exposing local server files in data lakehouse environments (Feedly). Community reaction has been measured, with no significant controversy or widespread alarm given the requirement for authenticated access and the absence of public exploits.