CVE-2026-102104 in Email Protection Gateway
Summary
by MITRE • 10/01/2026
Kiteworks Email Protection Gateway before version 9.5.0 is vulnerable to Server-Side Request Forgery (SSRF). A server-side request forgery (SSRF) weakness in Kiteworks Email Protection Gateway could allow a remote, unauthenticated attacker to induce the gateway to issue crafted requests to internal or otherwise unintended network destinations. The requests are triggered while the gateway performs an online certificate status check for an inbound message. Depending on the services reachable from the gateway, this could disclose sensitive internal information or disrupt gateway operation.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified in Kiteworks Email Protection Gateway versions prior to 9.5.0 represents a critical Server-Side Request Forgery (SSRF) flaw that compromises the integrity of the email security infrastructure. This weakness stems from insufficient validation of user-supplied input during the execution of online certificate status checks for inbound messages. When the gateway processes an incoming email, it is designed to verify the validity and revocation status of digital certificates associated with the message or its sender. However, due to a lack of strict constraints on the destination URLs provided by external entities, an attacker can manipulate these parameters to redirect the server's request logic toward internal network resources that are not intended for public access. This architectural oversight allows a remote, unauthenticated actor to force the gateway application to act as a proxy or pivot point within the organization's network topology.
From a technical perspective, the core issue lies in the handling of certificate validation requests. The system fails to enforce an allowlist of permitted domains or IP ranges for these outbound connections. Consequently, by crafting specific HTTP or HTTPS requests containing maliciously formatted URLs pointing to internal services such as database servers, administrative interfaces, cloud metadata endpoints, or other sensitive backend systems, an attacker can exploit this trust relationship. Since the request originates from the gateway itself, it often bypasses perimeter firewalls and network segmentation controls that would typically block direct external access to these internal assets. This effectively neutralizes many traditional defense-in-depth strategies relying on network isolation, as the malicious traffic appears legitimate because it is generated by a trusted application server operating within the protected zone.
The operational impact of this vulnerability is severe and multifaceted. Primarily, it enables unauthorized data exfiltration from internal systems that are otherwise isolated from the internet. Attackers can read sensitive configuration files, database contents, or proprietary information stored on internal web servers by instructing the gateway to fetch their content. Furthermore, depending on the specific services reachable through this SSRF vector, an attacker may be able to perform port scanning of the internal network, identify running services and their versions, or even interact with vulnerable internal applications to execute further attacks such as remote code execution if those services have known weaknesses. In worst-case scenarios, disrupting gateway operation is possible by targeting critical infrastructure components, leading to denial-of-service conditions that halt email processing for the entire organization.
This vulnerability aligns closely with Common Weakness Enumeration (CWE) ID 918, which defines Server-Side Request Forgery as a weakness where a web server receives a URL or similar request from an upstream component and retrieves the contents of it, but does not sufficiently ensure that the given data refers to a trusted resource. In terms of offensive security frameworks, this exploit maps directly to MITRE ATT&CK technique T1557, specifically Adversary-in-the-Middle (AitM), where attackers use compromised systems as proxies for lateral movement or credential harvesting. It also relates to T1046 Network Service Discovery, as the SSRF can be leveraged to map out internal network services and identify potential targets for subsequent exploitation phases within an intrusion kill chain.
Mitigation strategies must focus on immediate remediation through software updates and robust architectural hardening. The primary corrective action is to upgrade Kiteworks Email Protection Gateway to version 9.5.0 or later, where this specific input validation flaw has been addressed by the vendor. For environments where patching is not immediately feasible, network-level controls should be implemented to restrict outbound traffic from the gateway server. This includes configuring host-based firewalls on the gateway machine to allow only necessary connections to trusted certificate authority endpoints and blocking access to private IP address ranges such as 10.x.x.x, 172.16.x.x through 172.31.x.x, and 192.168.x.x. Additionally, implementing strict URL validation on the application layer that enforces a whitelist of allowed domains for certificate checks can provide an additional layer of defense against SSRF attempts until permanent fixes are deployed across all affected instances.