CVE-2026-102127 in Email Protection Gateway
Summary
by MITRE • 10/01/2026
An XML parser used by Kiteworks Email Protection Gateway did not restrict external entity references. Where an optional, non-default message-processing feature is enabled, a remote and unauthenticated sender could potentially use a crafted message to read files accessible to the gateway service account, including cryptographic key material and credentials, and have them sent to a destination they control.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified in Kiteworks Email Protection Gateway stems from an improper handling of external entity references within its XML parsing component. This flaw is classified under CWE-611, which describes Improper Restriction of XML External Entity Reference. In standard XML processing, parsers can be configured to resolve entities that reference external resources, such as files on the local system or remote URLs. When a parser fails to restrict these references by default or when specific features are enabled without adequate safeguards, it creates an avenue for attackers to exploit the parsing logic. The vulnerability specifically affects optional message-processing features within the gateway, meaning that exploitation requires certain configurations to be active, although this does not mitigate the severity given the potential impact on sensitive data.
From a technical perspective, the flaw allows a remote and unauthenticated attacker to craft malicious XML payloads embedded in email messages. By injecting specially constructed external entity declarations, an attacker can instruct the vulnerable parser to read arbitrary files from the server hosting the gateway service. The scope of accessible files is determined by the privileges of the account under which the gateway service operates. In many enterprise deployments, this service account may possess elevated permissions necessary for processing emails and integrating with directory services or storage systems. Consequently, the attacker can access critical system resources that are typically protected from external network traffic.
The operational impact of this vulnerability is severe due to the potential for unauthorized data exfiltration. An attacker who successfully exploits this flaw can read sensitive files accessible to the gateway service account. This includes cryptographic key material used for securing communications and credentials stored in configuration files or databases. Once these secrets are extracted, they can be transmitted to a destination controlled by the attacker via HTTP requests embedded within the XML payload. The compromise of cryptographic keys allows an adversary to decrypt previously captured traffic or impersonate legitimate services, while stolen credentials facilitate further lateral movement within the network. This aligns with ATT&CK technique T1005, which covers Data from Local System Retrieval, and potentially T1048 for Exfiltration Over Alternative Protocol if HTTP is used as the exfiltration channel.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary defense is to apply vendor-provided patches or updates that address this specific parsing flaw in Kiteworks Email Protection Gateway. Administrators should ensure that all optional message-processing features are updated to their latest secure versions. In the interim, if patching is not immediately feasible, organizations can implement network-level controls such as web application firewalls (WAF) to inspect and block XML payloads containing external entity references before they reach the parser. Additionally, enforcing strict input validation on any XML processing components and disabling unnecessary features that require complex parsing logic can reduce the attack surface. It is also critical to review service account permissions, ensuring that the gateway operates with the principle of least privilege, thereby limiting the files an attacker could access even if exploitation occurs. Regular audits of configuration settings and continuous monitoring for anomalous outbound traffic from the gateway servers are essential components of a defense-in-depth strategy against this type of vulnerability.