CVE-2025-46569: When OPA Paths Go Rogue - Rego Injection in the Data API

Robert Morgan

Robert Morgan

— 7 min read

Open Policy Agent (OPA) is the go-to engine for unifying policy enforcement across diverse stacks. But what happens when the path you query becomes the path to compromise? Buckle up, because CVE-2025-46569 reveals a sneaky Rego injection vulnerability lurking within OPA's Data API, potentially leading to Denial of Service (DoS) or unexpected policy outcomes. Let's dive in!

TL;DR / Executive Summary

What's the issue? CVE-2025-46569 is a path injection vulnerability in the Open Policy Agent (OPA) server's Data API. Attackers can craft malicious HTTP request paths that inject Rego code fragments into the policy query OPA constructs internally.
Affected Systems: OPA server deployments (not the Go library) versions prior to v1.4.0, particularly those exposed to untrusted environments without strict path validation in their authorization policies, or where upstream services allow unsanitized input into the OPA request path.
Severity: While a formal CVSS score isn't provided in the advisory, the impact includes potential Denial of Service (DoS) via resource exhaustion, "oracle attacks" (manipulating query success/failure to infer information or bypass checks), and potentially incorrect policy decisions under specific circumstances.
Mitigation: Upgrade OPA to version 1.4.0 or later. Implement strict path validation using OPA's own authorization policies or upstream controls (API Gateways). Limit OPA API exposure and use authentication.

Introduction: The Policy Engine's Double-Edged Sword

Open Policy Agent (OPA) has become a cornerstone of modern infrastructure, acting as a central decision-making engine. Need to know if user Alice can access resource X? Ask OPA. Need to validate a Kubernetes admission request? Ask OPA. It's powerful, flexible, and speaks the declarative language Rego.

One way to interact with an OPA server is through its RESTful APIs, notably the Data API (/v1/data/...). This API allows you to query for policy decisions or retrieve data stored within OPA. You specify what you want by providing a path, like /v1/data/myapp/policies/allow. OPA cleverly translates this path into a Rego query, something like data.myapp.policies.allow, evaluates it, and returns the result.

Simple, right? Mostly. But as CVE-2025-46569 demonstrates, this path-to-query translation mechanism, if not handled carefully, can be tricked. What if the path itself contained characters that broke out of the intended structure and injected arbitrary Rego code? This vulnerability matters because OPA often sits at critical control points; compromising its integrity, even subtly, can have significant security implications.

Technical Deep Dive: How a Path Becomes a Problem

Let's peek under the hood. When you send a GET request to, say, /v1/data/production/users/isAdmin, the OPA server needs to figure out which piece of policy or data corresponds to production/users/isAdmin.

Internally, OPA takes this path string and constructs a Rego reference. A reference is essentially a variable path in Rego, like data.production.users.isAdmin. This reference is then wrapped into a simple query that OPA's evaluation engine executes.

The Root Cause: The vulnerability lies in how OPA versions before 1.4.0 processed the URL path string when converting it into this internal Rego reference and query. It didn't sufficiently sanitize or validate the components of the path. Specifically, it didn't prevent URL-decoded path segments from containing characters like " (double quotes) or other Rego syntax elements that could prematurely terminate a string or introduce new logic.

Think of it like a classic SQL injection, but instead of injecting SQL, you're injecting Rego fragments. A carefully crafted path segment could look something like this (URL encoded): config%22%5D%3Btrue%3B%23. When URL decoded, this becomes config"];true;#.

If OPA naively constructed a query like data.some.prefix. + config"];true;#, the Rego parser might interpret this as:

  1. data.some.prefix["config"] - A valid reference using bracket notation.
  2. ; - A statement separator (though less common in simple queries).
  3. true - A boolean literal.
  4. ; - Another separator.
  5. # - Start of a comment (potentially ignoring subsequent legitimate parts of the path).

Attack Vectors & Business Impact:

  1. Denial of Service (DoS): An attacker could inject Rego code designed to be computationally expensive (e.g., complex comprehensions, recursive rules on large datasets). By sending requests with such paths, they could overload the OPA server, making it unresponsive to legitimate policy queries. This impacts any service relying on OPA for decisions.
    • Scenario: An attacker bombards an OPA-protected API gateway with requests having malicious paths, causing OPA to consume excessive CPU/memory, slowing down or blocking all API traffic.
  2. Oracle Attacks / Policy Bypass: While the advisory states the vulnerability cannot directly return arbitrary data, it can influence whether the constructed query succeeds or fails. An attacker could inject fragments like ; true to force a query that would normally fail (e.g., referencing non-existent data) to succeed, or ; false to force failure. This could be used to:
    • Probe the existence of certain data paths indirectly.
    • Potentially bypass authorization checks if the check relies solely on the successful evaluation of a specific path without validating the content of the result (less likely but possible in misconfigured policies).
    • Scenario: An authorization policy allows access if data.user.permissions[input.user] exists. An attacker crafts a path like user%22%5D%3Btrue%3B%23/permissions/someuser which might evaluate data.user["user"];true;#["permissions"]["someuser"]. Depending on the exact parsing and evaluation logic, the injected true could potentially influence the outcome, leading to an incorrect authorization decision. (Note: This is a theoretical illustration; the exact impact depends heavily on the OPA configuration and surrounding policies).

Who is affected? The advisory is clear: this primarily impacts standalone OPA servers exposed to untrusted networks without adequate authorization policies that perform exact path matching. If your OPA server only listens on localhost, or if you have a robust authorization policy validating input.path against an allow-list, you're likely safe from this specific vector. Also, if a service using OPA allows external input to form the request path to OPA without sanitization, that service introduces the risk.

Proof of Concept (Simplified Theoretical Example)

Let's illustrate with a simplified example. Imagine OPA has a simple policy:

package example.policy

allow := data.users[_].admin == true

A legitimate query to check for any admin user might target /v1/data/example/policy/allow. OPA internally might form a query like data.example.policy.allow.

Now, an attacker wants to cause trouble. They don't necessarily want allow, but maybe they want to probe or cause DoS. They craft a request path:

/v1/data/users%22%5D%3Bcount(data)%20%3E%2010000%3B%23/name

URL Decoded Path Segment: users"];count(data) > 10000;#

Intended OPA Action: Query data.users.name (or similar based on the full path).

Potential Malicious OPA Action (Pre-Patch): OPA might construct a query resembling data.users["users"];count(data) > 10000;#["name"].

Outcome:

  • The query structure is broken.
  • count(data) > 10000 gets injected. If data is large, this count operation could be expensive, contributing to DoS if repeated.
  • The # comments out the rest, potentially hiding errors or further path segments.
  • The overall query might fail unexpectedly or succeed based on the injected logic (count(data) > 10000), not the intended path lookup.

(Disclaimer: This is a simplified representation. The actual internal query construction and parsing behavior determine the precise outcome.)

Mitigation and Remediation: Patching the Path

Stopping this Rego-injection road trip involves several layers:

  1. Upgrade OPA (Primary Fix): Update your OPA server deployment to version 1.4.0 or later. This version contains the direct fix for the vulnerability.

  2. Patch Analysis - What Changed? Looking at the patch commit (ad2063247a14...), the core changes involve stricter handling of the path string:

    • Path Segment Validation: The stringPathToDataRef function (and its helper stringPathToRef) was modified to explicitly check for and reject path segments containing double quotes ("). Since quotes are used to delimit strings in Rego, allowing them in path segments used to build references was a key part of the injection vector. If a segment contains a quote, it now returns an error.
    • Stricter Query Parsing: A new function parseRefQuery was introduced. Instead of potentially concatenating strings and hoping the Rego parser does the right thing, the code now first parses the intended reference string (e.g., data.foo.bar) into an Abstract Syntax Tree (AST) body using ast.ParseBody. Crucially, parseRefQuery then validates that this parsed body contains exactly one expression, and that expression is only a simple reference (ast.Ref), not a function call, assignment, or other complex statement.
    • Using Parsed Queries: Functions like makeRego now use rego.ParsedQuery(query) with the validated query AST, instead of rego.Query(queryPath) which took the potentially injectable raw string. This ensures only simple, validated data references are evaluated via the Data API path mechanism.

  3. Workarounds & Defense-in-Depth: If upgrading immediately isn't possible, or for better security posture:

    • Limit Exposure: Don't expose the OPA server API directly to untrusted networks if possible. Keep it on localhost or within a trusted network boundary. OPA v1.0+ defaults to localhost, which is helpful.
    • Authentication: Require authentication for API access. While this doesn't fix the injection itself, it limits potential attackers to authenticated clients.
    • Authorization Policy for Paths: This is a powerful mitigation. Configure OPA with an authorization policy (--authorization=basic) that explicitly validates the input.path array against a list of known, safe paths.
    package system.authz

# Define exactly which API paths are allowed
allowed_paths := [
    ["v1", "data", "myapp", "policies", "allow"],
    ["v1", "data", "users", "profiles"],
    # Add all other legitimate paths used by your applications
]

# Default deny
default allow = false

# Allow if the requested path is in our list
allow {
    input.path in allowed_paths
}

    This policy ensures that only requests matching exactly the paths you expect are even processed by the Data API logic, effectively blocking any path manipulation attempts.

    • Upstream Validation: If another service (like an API Gateway or your own application) calls OPA, ensure that service validates or sanitizes the path components before making the request to OPA.

  4. Verification: After upgrading or applying workarounds, test with crafted paths (like the PoC example) to ensure they are rejected (e.g., return a 400 Bad Request or 403 Forbidden based on your authz policy) and don't cause excessive resource usage. Check OPA server logs for errors related to invalid paths or authorization failures.

Timeline

  • Discovery Date: Not specified in the advisory. (Likely early 2025 or late 2024)
  • Vendor Notification: Not specified.
  • Patch Availability: OPA v1.4.0 (Release date not specified, assumed shortly before or on public disclosure)
  • Public Disclosure: May 1, 2025 (Based on GitHub Advisory publish date)

Lessons Learned: Trust, but Verify (Your Inputs!)

This CVE serves as a great reminder of fundamental security principles:

  1. Input Validation is King: Never trust input, especially when it's used to construct code or queries in another language (SQL, Rego, shell commands, etc.). Always sanitize, validate, or use parameterized methods that separate data from code. The patch's move to parsing and validating the path before evaluation is a prime example.
  2. Defense in Depth: Relying solely on OPA's internal logic wasn't enough if exposed. Network controls (limiting exposure), Authentication (who can talk to OPA?), and Authorization (what can they ask?) provide crucial layers of security. The authorization policy workaround is particularly effective here.
  3. Understand Your Tools: Knowing how OPA translates API paths into Rego queries was key to understanding this vulnerability. Deeply understanding the tools and frameworks you use helps anticipate potential security pitfalls.

Key Takeaway: Even sophisticated policy engines like OPA are subject to classic injection vulnerabilities if input handling at the boundaries isn't meticulous. Treat every input as potentially hostile, especially when it crosses language or system boundaries.

References and Further Reading

Stay vigilant, validate those paths, and keep your policies secure!

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