Incorrect Calculation in github.com/open-policy-agent/opa
Date: 2022-02
Affected: go/github.com/open-policy-agent/opa
Attack vector: other
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2022-23628
CWE: CWE-682
CVSS: 6.3 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L)

### Impact Under certain conditions, pretty-printing an AST that contains synthetic nodes could change the logic of some statements by reordering array literals. Example of policies impacted are those that parse and compare web paths, see the example below. **All of these** three conditions have to be met to create an adverse effect: 1. An AST of Rego had to be **created programmatically** such that it ends up containing terms without a location (such as wildcard variables). 2. The AST had to be **pretty-printed** using the `github.com/open-policy-agent/opa/format` package. 3. The result of the pretty-printing had to be **parsed and evaluated again** via an OPA instance using the bundles, or the Golang packages. If any of these three conditions are not met, you are not affected. Notably, all three would be true if using **optimized bundles**, i.e. bundles created with `opa build -O=1` or higher. In that case, the optimizer would fulfil condition (1.), the result of that would be pretty-printed when writing the bundle to disk, fulfilling (2.). When the bundle was then used, we'd satisfy (3.). #### Example For example, the process outlined above could turn this rule ```rego hello { ["foo", _] = split(input.resource, "/") } ``` into ```rego hello { [_, "foo"] = split(input.resource, "/") } ``` with an input of ```rego { "resource": "foo/bar" } ``` the result would change from ```rego { "hello": true } ``` to (no default value of hello) ```rego {} ``` The sev


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