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The vulnerability resides in the PayPal webhook endpoint /extensions/paypal/webhook. When PayPal sends a webhook notification to this endpoint, it includes an HTTP header named `PAYPAL-CERT-URL` that contains the URL of the X.509 certificate used to verify the webhook signature. The affected application takes this header value and passes it directly into a server-side HTTP request via the `file_get_contents()` PHP function. No validation, allowlisting, or signature verification is performed on the header before it is used. This means an attacker can craft a malicious webhook request with an arbitrary `PAYPAL-CERT-URL` pointing to any external or internal destination. The server will then issue an HTTP GET request to that attacker‑controlled or internal URL. Because the response from the requested endpoint is not returned to the attacker, this is a blind SSRF. However, the attacker can still probe internal network services, scan for open ports, or interact with internal APIs that are not exposed to the public internet. The lack of any authentication requirement on the webhook endpoint makes this vulnerability exploitable by any remote unauthenticated attacker who can send a POST request to the webhook URL. The issue affects all versions of Paymenter prior to 1.5.0, where a fix was implemented. The vulnerability is classified as medium severity with a CVSS score of 5.3.
DailyCVE Form:
Platform: Paymenter
Version: <1.5.0
Vulnerability: Blind SSRF
Severity: Medium (5.3)
Date: 2026-06-22
Prediction: Patched in v1.5.0
What Undercode Say:
Analytics of this vulnerability show that the `PAYPAL-CERT-URL` header is trusted without any validation, making it a classic case of uncontrolled HTTP request destination. The following bash command can be used to simulate a malicious webhook request:
curl -X POST https://target.com/extensions/paypal/webhook \
-H "PAYPAL-CERT-URL: http://169.254.169.254/latest/meta-data/" \
-H "Content-Type: application/json" \
-d '{"event_type":"PAYMENT.CAPTURE.COMPLETED"}'
This command forces the server to fetch the AWS metadata endpoint, potentially exposing sensitive cloud instance information. The same technique can be used to probe internal services such as Redis, MySQL, or internal APIs.
Exploit:
An attacker can exploit this vulnerability by sending a crafted HTTP POST request to the webhook endpoint with a malicious `PAYPAL-CERT-URL` header. The server will then make a GET request to the supplied URL. Although the response is not directly returned, the attacker can use side‑channel techniques (e.g., timing differences, error messages, or DNS interactions) to infer information about internal services. For example, pointing the header to `http://localhost:8080/admin` could reveal whether an internal admin panel is reachable, or using `http://internal-service/health` could indicate service availability.
Protection:
To protect against this CVE, upgrade Paymenter to version 1.5.0 or later, which includes proper validation of the `PAYPAL-CERT-URL` header. If an immediate upgrade is not possible, implement a temporary mitigation by adding a network‑level allowlist that restricts outbound HTTP requests from the application to only known‑good domains (e.g., `.paypal.com` and .paypalobjects.com). Additionally, validate that the URL scheme is HTTPS and that the hostname matches an expected pattern before using it in file_get_contents().
Impact:
Successful exploitation allows an unauthenticated remote attacker to induce the server to make arbitrary HTTP GET requests to external or internal endpoints. This can lead to:
– Blind SSRF to attacker‑controlled systems, enabling further attacks such as phishing or malware distribution.
– Probing of internal network services, potentially exposing sensitive information about the internal infrastructure.
– In some configurations, access to internal services that are not otherwise accessible from the internet, which may lead to data exfiltration or privilege escalation.
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Sources:
Reported By: github.com
Extra Source Hub:
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