Summary
A critical server-side request forgery vulnerability in Kiteworks Email Protection Gateway may allow a remote, unauthenticated attacker to make the gateway send crafted requests to internal or otherwise unintended network destinations. The requests can be triggered when the gateway retrieves a certificate revocation list associated with an inbound message, potentially exposing internal information or disrupting gateway operations.
Affected context
The issue occurs in Kiteworks Email Protection Gateway deployments that retrieve certificate revocation lists while processing inbound messages. Risk depends on whether attacker-influenced certificate or revocation-list references are accepted and what internal services, metadata endpoints, or restricted network destinations are reachable from the gateway.
Exploit preconditions
- Attack surface: Inbound email and certificate revocation list retrieval functionality
- Required access: Remote network access to submit or influence an inbound message; authentication may not be required
- Trigger point: Gateway processing of the message and subsequent retrieval of the referenced certificate revocation list
- Why exploitation is possible: The gateway may issue outbound requests to attacker-influenced destinations without adequately restricting internal, loopback, private, or otherwise unintended network targets
Why this happens
The vulnerability is caused by insufficient validation and destination control for server-side requests generated during certificate revocation list retrieval. This maps to CWE-918: Server-Side Request Forgery, where application-side network functionality can be influenced to contact destinations that the attacker could not access directly. The insecure pattern is trusting externally derived URLs or network locations without enforcing a narrowly defined allowlist and safe redirect behavior.
Potential impact
- An attacker may access sensitive information exposed by internal services
- The gateway could be used to probe internal network destinations
- Cloud or infrastructure metadata may be disclosed where reachable
- Internal services may receive unintended requests
- Gateway availability or normal processing could be disrupted
General mitigation guidance
Mitigation typically focuses on reducing trust in externally supplied network locations and tightly controlling outbound requests.
Common defensive patterns include:
- Restricting certificate revocation list retrieval to approved schemes, hosts, and ports
- Blocking loopback, link-local, private, multicast, and other non-public address ranges
- Revalidating destinations after DNS resolution and across redirects
- Applying outbound network policies that limit gateway egress to required services
- Using short timeouts, response-size limits, and controlled redirect handling
- Running the gateway with minimal network and system privileges
- Logging and reviewing outbound retrieval destinations and unusual request failures
How teams detect issues like this
Organizations commonly detect SSRF risks through:
- Static analysis rules for externally influenced URL and HTTP-client usage
- Code review checks for missing destination validation, redirect controls, and IP-range filtering
- Dynamic testing with controlled internal endpoints and non-routable destinations
- Egress firewall and network-policy monitoring for unexpected gateway connections
- Alerts for requests to loopback, private, link-local, metadata, or unusual destination ranges
- Security policies requiring allowlisted outbound destinations for certificate and document retrieval
Automated review tools may help identify request-building paths that use untrusted message content.
