Summary
A server-side request forgery vulnerability in Kiteworks Email Protection Gateway can cause the gateway to send attacker-influenced requests to internal or otherwise unintended network destinations while retrieving an issuer certificate from an inbound message.
A remote, unauthenticated attacker may exploit this behavior to access sensitive internal information or disrupt services reachable from the gateway.
Affected context
The issue occurs in deployments where the gateway processes inbound messages and retrieves issuer certificates as part of message or certificate handling. Risk is increased when the gateway can reach internal services, cloud metadata endpoints, administrative interfaces, or other destinations that are not intended to be accessible through external message processing.
Exploit preconditions
- Attack surface: Inbound email or message-processing functionality exposed by the gateway
- Required access: No authentication may be required; the attacker needs to submit or cause processing of a crafted inbound message
- Trigger point: Issuer certificate retrieval during inbound message handling
- Network condition: The gateway must have network connectivity to an unintended destination
- Why exploitation is possible: Attacker-influenced certificate retrieval can cause server-side requests to destinations outside the intended trust boundary
Why this happens
The vulnerability results from insufficient validation and restriction of a server-side network request initiated during issuer certificate retrieval. When externally influenced data affects the destination of a backend request without strong allowlisting and network boundary enforcement, the server can be used as a proxy to reach internal or otherwise restricted resources.
This behavior maps to CWE-918: Server-Side Request Forgery, in which untrusted input influences requests made from a trusted server-side component.
Potential impact
- An attacker may obtain sensitive information from reachable internal services
- Internal administrative or monitoring endpoints could be accessed
- Cloud or infrastructure metadata could be exposed where reachable
- Requests could cause disruption or resource exhaustion in internal services
- The gateway's network position could enable reconnaissance of protected infrastructure
General mitigation guidance
Mitigation generally focuses on reducing trust in externally influenced request destinations and limiting the gateway's network reach.
Common defensive patterns include:
- Restricting certificate and network retrieval to approved schemes, hosts, ports, and destinations
- Using explicit allowlists rather than accepting arbitrary URLs or endpoint references
- Validating redirects and preventing DNS or address resolution from bypassing destination controls
- Blocking access from the gateway to private, loopback, link-local, metadata, and management networks unless specifically required
- Applying egress filtering and network segmentation around the gateway
- Running certificate retrieval with minimal privileges and isolated network permissions
- Using bounded timeouts, response-size limits, and safe failure behavior for outbound requests
How teams detect issues like this
Organizations can identify SSRF risks through:
- Static analysis for HTTP clients or certificate-fetching routines that use externally derived destinations
- Code review checks for missing URL parsing, scheme validation, host allowlisting, redirect validation, and private-address blocking
- Runtime monitoring of unusual outbound connections from the gateway, especially to private ranges, metadata services, or administrative ports
- Egress firewall policies that alert on or deny unexpected destinations
- Application and proxy logs correlating inbound message processing with outbound network requests
- Automated security review tools that flag server-side requests using untrusted input
