CVE-2020-36851 Rob--W cors-anywhere Misconfigured CORS Proxy Allows SSRF
Misconfigured CORS proxies allow attackers to perform Server-Side Request Forgery, accessing internal services and stealing cloud credentials.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2020-36851?
CVE-2020-36851 is a critical server-side request forgery vulnerability in Rob--W / cors-anywhere, published on 25 Sep 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2020-36851?
2 open source packages ship an affected version, including cors-anywhere.
| Package | Affected | Fixed in |
|---|---|---|
cors-anywhere npm | All versions to 0.4.4 | None |
cors-anywhere npm | All versions to 0.4.4 | None |
How do I fix CVE-2020-36851?
Change a configuration setting.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2020-36851 being exploited?
There is no known exploitation of CVE-2020-36851 in the wild and no public exploit code.
Sources
Also known as GHSA-r3jv-xfgx-gj24, ROOT-APP-NPM-CVE-2020-36851.