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Cedar: JSON template is in scope missing slot-id validation allows link panic and decision divergence

Low severity GitHub Reviewed Published Jun 25, 2026 in cedar-policy/cedar • Updated Oct 29, 2026

Package

npm @cedar-policy/cedar-wasm (npm)

Affected versions

>= 4.0.1, < 4.11.1
>= 3.2.0, < 3.4.3

Patched versions

4.11.1
3.4.3
cargo cedar-policy (Rust)
>= 4.0.0, < 4.11.1
>= 3.0.0, < 3.4.3
4.11.1
3.4.3

Description

Cedar 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

References

@katherine-hough katherine-hough published to cedar-policy/cedar Jun 25, 2026
Published to the GitHub Advisory Database Oct 29, 2026
Reviewed Oct 29, 2026
Last updated Oct 29, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required High
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability Low
Subsequent System Impact Metrics
Confidentiality Low
Integrity Low
Availability Low

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:L/SI:L/SA:L

EPSS score

Weaknesses

Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-c33x-vcv4-vg3g

Source code

Credits

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