Cedar: JSON template is in scope missing slot-id validation allows link panic and decision divergence — cedar-policy
Improper Input ValidationCedar users must be using all of the following features to be affected by this advisory: JSON format policies, policy templates, and the is in scope condition. This advisory only affects JSON-formatted Cedar policy templates containing is in scope conditions that are malformed according to the Cedar syntax. It does not affect syntactically well-formed policies.
Users of Cedar who author policies in the JSON format were able to write Cedar policies using the is in condition with an incorrect slot identifier in the principal and resource scope constraints (e.g., ?principal in the resource scope constraint) even though this is not allowed when parsing policies from the Cedar policy syntax. Internally, the slot identifiers were silently corrected (e.g. ?resource is placed in the resource scope constraint).
If the policy contains exactly one slot in either the principal or resource position, then any attempt to create a linked policy from the template results in an error: the internal representation of the template does not contain the slot identifier as written in the malformed JSON policy (it has been corrected silently), so attempting to fill that slot is an error. If instead the template is linked using slot identifier expected internally (i.e., not what is written in the JSON template), the linking will initially succeed, but a subsequent invariant violation will cause a panic.
When the template contains slots in both the principal and resource position, then both slots will be present in the internal representation: linking succeeds, but with each slot bound to the value intended for the other (the silent correction). The linked policy is then semantically different from the malformed policy the user intended, and any subsequent authorization decision made against that policy may lead to accesses being unintentionally allowed or denied.
Concretely, consider the following JSON format policy template intended to deny users in a particular project from accessing documents with a particular classification.
{
"effect": "forbid",
"principal": {
"op": "is",
"entity_type": "User",
"in": { "slot": "?resource" }
},
"action": { "op": "All" },
"resource": {
"op": "is",
"entity_type": "Doc",
"in": { "slot": "?principal" }
},
"conditions": []
}
Linked with ?principal = Classification::"topsecret" and ?resource = Project::"alpha", the author expects to create the policy:
forbid(principal is User in Project::"alpha", action, resource is Doc in Classification::"topsecret");
But because Cedar internally links slots by scope position (not by name), the actual policy evaluated by the engine is:
forbid(principal is User in Classification::"topsecret", action, resource is Doc in Project::"alpha");
If a user is in Project::"alpha" but not Classification::"topsecret", the forbid policy does not apply, and access is unintentionally allowed.
Patches
This advisory is patched in version 4.11.1 and 3.4.3, both available on Crates.io and NPM.
Workarounds
If you cannot update to a patched version, you can determine if you are affected by checking your JSON format policy templates for the following two patterns.
"principal": {
"op": "is",
"entity_type": "User",
"in": { "slot": "?resource" }
}
and
"resource": {
"op": "is",
"entity_type": "Doc",
"in": { "slot": "?principal" }
}
References
| Software | Affected versions |
|---|---|
cedar-policy
|
>= 4.0.0, < 4.11.1 |
|
cedar-policy
|
>= 3.0.0, < 3.4.3 |
@cedar-policy / cedar-wasm
|
>= 4.0.1, < 4.11.1 |
|
@cedar-policy / cedar-wasm
|
>= 3.2.0, < 3.4.3 |
Is cedar-policy exposed on your perimeter?
A vulnerability database tells you what is broken. Attack surface management tells you where it is running: it discovers your internet-facing assets and flags the ones affected by issues like this one.
What is attack surface management? →
Deep Security Visibility Without the Complexity
SynScan provides clear, real-time security insights so you can monitor your attack surface, spot risks early, and act fast—without extra complexity.
- No setup fees
- 5-min deployment
- Cancel anytime
Frequently Asked Questions
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.