---
title: "CVE-2020-36851: cors-anywhere vulnerable to server-side request forgery"
url: https://erroneo.us/security/cve/CVE-2020-36851/
description: "CVE-2020-36851 (cors-anywhere (npm)): Rob--W cors-anywhere instances configured as an open proxy allow unauthenticated external users to induce the server…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-09-25
date_modified: 2026-10-08
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2020-36851"
kev: false
cvss: 9.5
epss: 0.00828
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2020-36851: cors-anywhere vulnerable to server-side request forgery

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.8% , percentile 57: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 57% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes cors-anywhere (npm) <= 0.4.4, no fixed version listed . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- npm `cors-anywhere` <= 0.4.4 → fixed: none listed

## Affected products (CVE record)

- Rob--W / cors-anywhere Rob--W / cors-anywhere: <= 0.4.4

## Severity

- VulnCheck CVSS 4.0: 9.5 `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`
- GitHub CVSS 4.0: 9.0 `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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.83% probability of exploitation activity in the next 30 days; percentile 57.

## Sources

- [github.com](https://github.com/SocketDev/security-research/security/advisories/GHSA-9wmg-93pw-fc3g)
- [GitHub Advisory GHSA-r3jv-xfgx-gj24](https://github.com/advisories/GHSA-r3jv-xfgx-gj24)
- [CVE.org record CVE-2020-36851](https://www.cve.org/CVERecord?id=CVE-2020-36851)
- [NVD entry CVE-2020-36851](https://nvd.nist.gov/vuln/detail/CVE-2020-36851)
- [github.com](https://github.com/Rob--W/cors-anywhere/issues/152)
- [github.com](https://github.com/Rob--W/cors-anywhere/issues/78)
- [certik.com](https://www.certik.com/resources/blog/cors-anywhere-dangers-of-misconfigured-third-party-software)
- [vulncheck.com](https://www.vulncheck.com/advisories/rob-w-cors-anywhere-misconfigured-cors-proxy-allows-ssrf)
- [github.com](https://github.com/Rob--W/cors-anywhere/issues/521)

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Source page: https://erroneo.us/security/cve/CVE-2020-36851/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt