cors-anywhere vulnerable to server-side request forgery

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

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 · score source

EPSS

• CVE-2020-36851: 0.83% estimated exploitation activity in the next 30 days; percentile 57.56 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

25 Sep 2025, 15:30 UTC

Last modified by the source

4 May 2026, 08:43 UTC

Source last checked

26 Oct 2026, 12:38 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-r3jv-xfgx-gj24

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-r3jv-xfgx-gj24

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# Patch Next advisory brief: CVE-2020-36851

Advisory: cors-anywhere vulnerable to server-side request forgery
IDs: CVE-2020-36851, GHSA-r3jv-xfgx-gj24
Record: https://patchnext.com/advisories/cve-2020-36851 (revision 3, source checked 26 Oct 2026, 12:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm cors-anywhere: affected <= 0.4.4

## Suggested inspection (read-only)
- `npm ls cors-anywhere --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on cors-anywhere.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-r3jv-xfgx-gj24 (OSV record GHSA-r3jv-xfgx-gj24 lists affected ranges: npm cors-anywhere >=0 <=0.4.4)
- Verified: https://github.com/advisories/GHSA-r3jv-xfgx-gj24 (GitHub-reviewed advisory GHSA-r3jv-xfgx-gj24 lists affected ranges: npm cors-anywhere >=0 <=0.4.4)

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