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Nuxt: `__nuxt_island` endpoint does not bind responses to request props, enabling shared-cache poisoning

Low severity GitHub Reviewed Published May 18, 2026 in nuxt/nuxt • Updated May 19, 2026

Package

npm @nuxt/nitro-server (npm)

Affected versions

>= 3.20.0, <= 3.21.5
>= 4.2.0, <= 4.4.5

Patched versions

3.21.6
4.4.6
npm nuxt (npm)
>= 3.1.0, <= 3.21.5
>= 4.0.0-alpha.1, <= 4.4.5
3.21.6
4.4.6

Description

Summary

The /__nuxt_island/* endpoint accepts attacker-controlled props query/body parameters and renders any island component without verifying that the URL-resident hash (<Name>_<hashId>.json) was actually issued for those inputs by <NuxtIsland>. The hash is computed and embedded client-side but never validated server-side, so the same path can return materially different responses depending on the query.

Island components are documented as rendering independently of route context - page middleware does not apply to them, and they are intentionally cacheable as a function of their props. This advisory does not treat that contract as a vulnerability. It treats the absence of a binding between the URL the cache keys on and the response served at that URL as one.

Impact

In applications where a CDN or reverse-proxy in front of the app caches /__nuxt_island/* keyed by path only (ignoring query) - a documented misconfiguration class, see GHSA-jvhm-gjrh-3h93 - an attacker can prime the cache for a path with their own choice of props, and subsequent users requesting the same path receive the attacker's rendered HTML rather than the response intended for them. The cache entry persists until normal expiry.

Where the affected island has any prop flowing into an unsafe HTML sink in application code (v-html, innerHTML, a third-party renderer treating a prop as HTML), this becomes stored XSS in the embedding page's origin until the cache entry expires. HttpOnly cookies remain out of reach but anything else in the origin (other cookies, in-origin requests, DOM state) is reachable by the injected script.

Preconditions:

  • experimental.componentIslands enabled (or the default 'auto' with at least one server / island component in the app).
  • A shared intermediary cache (CDN, reverse-proxy, edge cache) keyed on path only.
  • For the XSS pivot specifically: an application-authored island that puts a prop through an unsafe HTML sink.

Without the second precondition, the response shape is per-request and unaffected. Without the third, the worst case is content-swap / inert HTML injection rather than script execution.

Patches

Patched in nuxt@4.4.6 and nuxt@3.21.6 by #35077. The island handler now recomputes the expected hashId from (name, props, context) using the same ohash function <NuxtIsland> already uses to embed the hash in the URL, and rejects requests (HTTP 400) whose URL-resident hash does not match. The response is now a pure function of the request path: a path-keyed shared cache returns the correct response to every requester for that path, and an attacker cannot synthesise a path whose hash matches arbitrary props.

Workarounds

For users unable to upgrade immediately:

  • Ensure any intermediary cache keys /__nuxt_island/* on the full query string, not on the path alone. This is the recommended configuration regardless.
  • Audit application-authored islands for props flowing into v-html / innerHTML / similar HTML sinks; treat island props as untrusted user input.

Note on island authentication

Important

It's important to remember that route middleware does not run when rendering island components, and islands cannot rely on routing-layer auth. Applications gating sensitive data behind page middleware should enforce that auth inside the island's own data layer (server-only routes, useRequestEvent + manual session checks, etc.) rather than relying on the embedding page's middleware - this was true before this advisory and remains true after it.

A separate advisory addresses *.server.vue pages registered as page_<routeName> islands, where the documented "middleware doesn't run for islands" contract collides with the page's own definePageMeta({ middleware }) declaration in a way that constitutes a genuine bug rather than documented behaviour.

References

@danielroe danielroe published to nuxt/nuxt May 18, 2026
Published to the GitHub Advisory Database May 19, 2026
Reviewed May 19, 2026
Last updated May 19, 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 None
User interaction Passive
Vulnerable System Impact Metrics
Confidentiality Low
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality Low
Integrity Low
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:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

EPSS score

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

Acceptance of Extraneous Untrusted Data With Trusted Data

The product, when processing trusted data, accepts any untrusted data that is also included with the trusted data, treating the untrusted data as if it were trusted. Learn more on MITRE.

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. Learn more on MITRE.

CVE ID

CVE-2026-46342

GHSA ID

GHSA-g8wj-3cr3-6w7v

Source code

Credits

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