Rob--W cors-anywhere Misconfigured CORS Proxy Allows SSRF
Summary
| CVE | CVE-2020-36851 |
|---|---|
| State | PUBLISHED |
| Assigner | VulnCheck |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2025-09-25 15:16:01 UTC |
| Updated | 2026-05-26 14:16:24 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 9.5 CRITICAL from [email protected]
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:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS: 0.008240000 probability, percentile 0.747320000 (date 2026-05-28)
Problem Types: CWE-918 | CWE-942 | CWE-942 CWE-942 Permissive Cross-domain Policy with Untrusted Domains | CWE-918 CWE-918 Server-Side Request Forgery (SSRF)
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 9.5 | CRITICAL | 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:X/C... |
| 4.0 | CNA | CVSS | 9.5 | CRITICAL | 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 |
CVSS v4.0 Breakdown
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:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Rob--W Cors-anywhere | Rob--W / Cors-anywhere | affected 0.4.4 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/Rob--W/cors-anywhere/issues/521 | [email protected] | github.com | |
| github.com/SocketDev/security-research/security/advisories/GHSA-9wmg-93p... | [email protected] | github.com | |
| www.vulncheck.com/advisories/rob-w-cors-anywhere-misconfigured-cors-proxy-allow... | [email protected] | www.vulncheck.com | |
| github.com/Rob--W/cors-anywhere/issues/152 | [email protected] | github.com | |
| github.com/Rob--W/cors-anywhere/issues/78 | [email protected] | github.com | |
| www.certik.com/resources/blog/cors-anywhere-dangers-of-misconfigured-third-p... | [email protected] | www.certik.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: CertiK's Pentesting Team (en)
CNA: Jonathan Leitschuh (en)
Additional Advisory Data
Workarounds
CNA: 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.