CVE-2020-36851: Cors anywhere Cors-anywhere Vulnerable To Server-side Request Vulnerability
CRITICALCVE-2020-36851 is a CRITICAL cors-anywhere vulnerable to server-side request vulnerability (CWE-918: Server-Side Request Forgery (SSRF)) affecting Cors anywhere libraries in the npm ecosystem. The issue involves cors-anywhere vulnerable to server-side request forgery. Remediation is available in the latest vendor maintenance releases.
CVE-2020-36851 at a Glance
How to Fix CVE-2020-36851
To remediate this vulnerability, upgrade all affected Cors anywhere dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install cors-anywhere@Latest secure releaseRun the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls cors-anywhereHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2020-36851, inspect your project dependencies using npm:
npm ls cors-anywhereAnalyze the terminal output to locate any version of Cors anywhere in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.
Note: The npm ls cors-anywhere command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-918: Server-Side Request Forgery (SSRF), where the web server receives a url or similar request from an upstream component and retrieves the contents of this url, but it does not sufficiently ensure that the request is being sent to the expected destination. In Cors anywhere, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2020-36851 Affected Cors anywhere Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
cors-anywhere
|
npm |
≤ 0.4.4
|
|
References
Frequently Asked Questions
What is CVE-2020-36851?
Which Cors anywhere versions are affected?
What version fixes CVE-2020-36851?
Is cors-anywhere affected?
What CWE is associated with CVE-2020-36851?
How can I check npm dependencies for CVE-2020-36851?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-r3jv-xfgx-gj24",
"modified" : "2025-09-26T16:34:55Z",
"published" : "2025-09-25T15:30:24Z",
"aliases" : [ "CVE-2020-36851" ],
"summary" : "cors-anywhere vulnerable to server-side request forgery",
"details" : "Rob -- W / cors-anywhere instances configured as an open proxy allow unauthenticated external users to induce the server to make HTTP requests to arbitrary targets (SSRF). Because the proxy forwards requests and headers, an attacker can reach internal-only endpoints and link-local metadata services, retrieve instance role credentials or other sensitive metadata, and interact with internal APIs and services that are not intended to be internet-facing. The vulnerability is exploitable by sending crafted requests to the proxy with the target resource encoded in the URL; many cors-anywhere deployments forward arbitrary methods and headers (including PUT), which can permit exploitation of IMDSv2 workflows as well as access to internal management APIs. Successful exploitation can result in theft of cloud credentials, unauthorized access to internal services, remote code execution or privilege escalation (depending on reachable backends), data exfiltration, and full compromise of cloud resources. Mitigation includes: restricting the proxy to trusted origins or authentication, whitelisting allowed target hosts, preventing access to link-local and internal IP ranges, removing support for unsafe HTTP methods/headers, enabling cloud provider mitigations, and deploying network-level protections.",
"severity" : [ {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:H/E:P"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "cors-anywhere"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"last_affected" : "0.4.4"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/SocketDev/security-research/security/advisories/GHSA-9wmg-93pw-fc3g"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-36851"
}, {
"type" : "WEB",
"url" : "https://github.com/Rob--W/cors-anywhere/issues/152"
}, {
"type" : "WEB",
"url" : "https://github.com/Rob--W/cors-anywhere/issues/521"
}, {
"type" : "WEB",
"url" : "https://github.com/Rob--W/cors-anywhere/issues/78"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/Rob--W/cors-anywhere"
}, {
"type" : "WEB",
"url" : "https://www.certik.com/resources/blog/cors-anywhere-dangers-of-misconfigured-third-party-software"
}, {
"type" : "WEB",
"url" : "https://www.vulncheck.com/advisories/rob-w-cors-anywhere-misconfigured-cors-proxy-allows-ssrf"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-918" ],
"severity" : "CRITICAL",
"github_reviewed" : true,
"github_reviewed_at" : "2025-09-25T16:47:59Z",
"nvd_published_at" : "2025-09-25T15:16:01Z"
}
}