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Apollo Router Core: Browser Bug Enables Bypass of XS-Search Prevention via Read-Only Cross-Site Request Forgery

Moderate severity GitHub Reviewed Published Mar 24, 2026 in apollographql/router

Package

cargo apollo-router (Rust)

Affected versions

>= 2.11.0, < 2.12.1
>= 2.0.0, < 2.10.2
< 1.61.13

Patched versions

2.12.1
2.10.2
1.61.13

Description

Impact

In a Cross-Site Request Forgery attack, untrusted web content causes browsers to send authenticated requests to web servers which use cookies for authentication. While the web content is prevented from reading the request's response due to the Cross-Origin Request Sharing (CORS) protocol, the attacker may be able to cause side effects in the server ("CSRF" attack), or learn something about the response via timing analysis ("XS-Search" attack).

Apollo Router has a built-in feature which prevents CSRF and XS-Search attacks: it refuses to process GraphQL requests that could possibly have been sent by a spec-compliant web browser without a protective "preflight" step. See Apollo Router's docs for more details on CORS, CSRF attacks, and Apollo Router's CSRF prevention feature.

This feature is fully effective against attacks carried out against users of spec-compliant browsers. Unfortunately, a major browser introduced a bug in 2025 which meant in certain cases, it failed to follow the CORS spec. The browser's maintainers have already committed to fixing the bug and making the browser spec-compliant again.

Even with this bug, Apollo Router's CSRF prevention feature blocks "side effect" CSRF attacks: Apollo Router will still correctly refuse to execute mutations in requests that were not preflighted. However, some specially crafted authenticated GraphQL queries can be issued across origins without preflight in buggy versions of this browser, allowing for XS-Search attacks: an attacker can analyze response times to learn facts about the responses to requests such as whether fields return null or approximately how many list entries are returned from fields.

Apollo Router installations are only vulnerable if they rely on cookies (or HTTP Basic Auth) for authentication.

Patches

The vulnerability is patched in the following versions of Apollo Router:

These releases contain a single change: GraphQL requests sent in HTTP GET requests which contain a Content-Type header naming a type other than application/json are rejected. (GET requests with no Content-Type are allowed.) This change prevents XS-Search attacks even in browsers which are non-compliant in ways similar to this browser.

There are no known cases where GraphQL apps depend on the ability of clients to send non-empty Content-Type headers with GET requests other than application/json, so this change has not been made configurable; if this change breaks a specific use case, contact support and more configurability can be added.

Workarounds

If upgrading is not possible, this particular browser's bug can be mitigated by preventing any HTTP request with a Content-Type header containing message/ from reaching the Apollo Router (e.g. in a load balancer/proxy).

If the load balancer cannot easily be updated to block these requests, it can also be done with a Rhai script within Router:

# config.yaml
rhai:
  scripts: "/directory/with/rhai/script"
  main: "main.rhai"

# main.rhai
fn router_service(service) {
    const request_callback = Fn("process_request");
    service.map_request(request_callback);
}

fn process_request(request) {
    if "content-type" in request.headers {
        if request.headers["content-type"].contains("message/") {
            throw "Error: invalid content type"
        }
    }
}

While the patch prevents a broader class of similar issues, the only known way to exploit this vulnerability is against a particular browser which currently plans to ship a fix in May 2026. If it is already past June 2026 and this vulnerability has not been addressed yet, it is likely that the installation is not currently vulnerable. Upgrading to the latest version of Apollo Router is still recommended for the broader protection.

Resources

The browser bug causes a similar vulnerability in Apollo Server; see https://github.com/apollographql/apollo-server/security/advisories/GHSA-9q82-xgwf-vj

References

@glasser glasser published to apollographql/router Mar 24, 2026
Published to the GitHub Advisory Database Mar 26, 2026
Reviewed Mar 26, 2026

Severity

Moderate

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 High
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality Low
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality Low
Integrity None
Availability None

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:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N

EPSS score

Weaknesses

Exposure of Sensitive Information to an Unauthorized Actor

The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-hff2-gcpx-8f4p

Source code

Credits

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