CVE-2026-31226 — OS command injection in TinyZero / verl HDFS copy utilities

MITRE service request: 1987825

Status: RESERVED (pending a qualifying public reference per CNA Rules §5.3).

Official CVE description

The TinyZero project thru commit 6652a63c57fa7e5ccde3fc9c598c7176ff15b839 (2025-58-24) contains a critical command injection vulnerability (CWE-78) in its HDFS file operation utilities. The vulnerability arises from the unsafe construction and execution of shell commands via os.system() without proper input sanitization or escaping. User-controlled input (such as file paths) is directly interpolated into shell command strings using f-strings within the _copy() function. An attacker can inject arbitrary OS commands by supplying a specially crafted path parameter through the Hydra configuration framework. This leads to remote code execution with the privileges of the user running the TinyZero training process.

Summary

Hydra CLI overrides propagate user-controlled actor_rollout_ref.model.path (and similar) values into verl filesystem helpers. hdfs_io._copy() builds hdfs dfs -cp -f {from_path} {to_path} with f-strings and passes the result to os.system(), so shell metacharacters in the path fragment execute arbitrary commands.

Affected product and versions

Technical details

Risk

Critical for shared clusters where trainees can override Hydra configs.

Remediation / workaround