CVE-2026-102103 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 retrieves a certificate revocation list in 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 prior to version 9.5.0 represents a critical Server-Side Request Forgery (SSRF) flaw that compromises the integrity of email security infrastructure by exploiting how the system handles certificate revocation list retrieval during inbound message processing. This weakness stems from insufficient validation of user-supplied input or internal configuration parameters used when the gateway attempts to verify digital certificates associated with incoming emails. By manipulating these inputs, a remote attacker who does not require authentication can force the application server to initiate HTTP requests to arbitrary destinations that are outside the intended scope of operation. The core technical failure lies in the lack of strict allow-listing or rigorous validation mechanisms for URLs and IP addresses processed during the certificate revocation check phase, allowing an adversary to redirect these internal system calls toward sensitive backend services, local host interfaces, or other resources within the protected network perimeter that would otherwise be inaccessible from external networks.
From a technical perspective, this SSRF vulnerability allows an unauthenticated actor to leverage the gateway as a proxy for malicious requests. When processing inbound messages, the email protection gateway interacts with Certificate Revocation List (CRL) distribution points to ensure the validity of sender certificates. If the CRL URL or related parameters are not properly sanitized, an attacker can craft specific payloads that cause the server to fetch resources from internal networks such as database servers, administrative interfaces, cloud metadata endpoints, or other microservices running on localhost or private subnets. This capability effectively bypasses network perimeter defenses because the requests originate from a trusted and authorized system component rather than directly from the external internet. The attacker can potentially read sensitive data returned by these internal services, including configuration files, database contents, or authentication tokens, thereby gaining deep insight into the organization's infrastructure architecture and security controls.
The operational impact of this vulnerability is severe, as it facilitates both information disclosure and potential service disruption depending on the specific services reachable from the gateway environment. If critical internal APIs are exposed through the SSRF vector, attackers may extract proprietary data or credentials that could lead to further lateral movement within the network. Furthermore, by directing requests toward unstable or resource-intensive internal endpoints, an attacker could induce denial of service conditions against those specific services, disrupting email processing capabilities and affecting business continuity. The ability to interact with cloud metadata services is particularly dangerous in modern deployments, as it may allow the extraction of instance-specific credentials that grant access to broader cloud resources, escalating the scope of compromise beyond the immediate gateway appliance.
This vulnerability aligns closely with CWE-918, which defines Server-Side Request Forgery weaknesses where a web server receives a URL or similar request from an end user and makes requests using that data without proper validation. Additionally, in terms of offensive security frameworks such as MITRE ATT&CK, this behavior corresponds to techniques involving T1560, specifically the use of Archive Collected Data via tools like curl or wget executed through server-side processes, and potentially T1078 if used for initial access or persistence by leveraging extracted credentials. The lack of authentication requirement classifies it under high-severity remote exploitation vectors that do not require prior compromise of user accounts.
To mitigate this risk, organizations must immediately upgrade to Kiteworks Email Protection Gateway version 9.5.0 or later where the flaw has been addressed through enhanced input validation and strict URL allow-listing for certificate revocation checks. Until patching is complete, network-level controls should be implemented to restrict outbound traffic from the gateway server to only known and necessary external CRL distribution points, blocking access to internal IP ranges and cloud metadata endpoints such as 169.254.169.254 for AWS or similar addresses for other providers. Implementing web application firewalls with SSRF detection rules can also provide an additional layer of defense by inspecting outbound request patterns for anomalies indicative of exploitation attempts, ensuring that the gateway operates within its intended security boundary and preventing unauthorized access to internal network resources.