zrok ProxyShare SSRF Vulnerability (CVE-2026-45568)

The zrok Python SDK, specifically the ProxyShare functionality, is susceptible to a server-side request forgery (SSRF) vulnerability, identified as CVE-2026-45568. This flaw exists due to the use of urllib.parse.urljoin without proper sanitization of the input path. An attacker can exploit this by crafting a request containing an absolute URL in the path. The Flask handler then passes this malicious path to urljoin, which incorrectly combines it with the target URL. This results in the proxy forwarding the request to an attacker-controlled server instead of the intended target, potentially leading to information disclosure or internal network access. The vulnerability affects zrok versions 0.4.47 through 1.1.11. This matters for defenders because it allows an attacker to bypass intended access controls and potentially gain access to internal resources.

Attack Chain

1. Alice configures a zrok ProxyShare with a defined target URL, for example, https://internal-api.example.com.
2. Bob identifies the exposed ProxyShare endpoint.
3. Bob crafts a malicious request to the ProxyShare endpoint, including an absolute URL in the path, such as /http://127.0.0.1:19190/metadata.
4. The Flask application routes the request to the proxy function.
5. The proxy function uses urllib.parse.urljoin(self.target, path) to construct the outbound URL. Due to the absolute URL in path, urljoin resolves to http://127.0.0.1:19190/metadata instead of a URL on Alice’s intended target.
6. The requests.request function sends the crafted request to the attacker-controlled URL (http://127.0.0.1:19190/metadata).
7. The attacker’s server (127.0.0.1:19190) receives the request, potentially including sensitive information or internal headers.
8. The attacker’s server responds, and the response is relayed back to Bob, completing the SSRF attack.

Impact

Successful exploitation of CVE-2026-45568 allows an attacker to perform SSRF attacks against zrok deployments. This can enable the attacker to access internal services, read sensitive data from internal endpoints, or potentially perform actions on behalf of the zrok server. The impact can range from information disclosure to full compromise of internal systems, depending on the services accessible from the zrok server.

Recommendation

• Upgrade zrok to a version beyond 1.1.11 to patch CVE-2026-45568.
• Deploy the Sigma rule “Detect zrok SSRF Attempt via Absolute URL in Request Path” to detect exploitation attempts against vulnerable zrok instances.
• Monitor web server logs for requests containing absolute URLs in the path to the zrok proxy endpoint to identify potential SSRF attempts, referencing the attack chain described above.