Horizon Alert
Summary of the vulnerability and why it matters
This advisory details a vulnerability in FreeRDP's handling of WebSocket connections, specifically how a malicious gateway could cause the client to disclose sensitive information or crash. The issue lies in how the client responds to specific network traffic, potentially exposing system details or causing a denial of service. The primary concern is to determine if this specific component is used and exposed within our environment.
- A security flaw in FreeRDP can leak data or crash.
- Affects how clients handle specific network messages.
- Confirm relevance and potential exposure within our systems.
Attack Path
How an attacker could exploit the issue
An attacker could exploit this vulnerability by interacting with a FreeRDP client that handles a WebSocket gateway transport. The attacker would need to send a specially crafted Ping control frame to the client. This would cause the client to respond with an overlong Pong frame, potentially disclosing sensitive information or crashing the client.
- Network access required.
- Malicious WebSocket peer triggers vulnerability.
- Information disclosure or denial of service.
Live Threat
Current exploitation, exposure, and threat context
A malicious gateway or WebSocket peer could send a crafted Ping control frame, causing a FreeRDP client to disclose memory contents beyond the expected response. This could potentially reveal sensitive information like the masking key, which is used to unmask the reply. In other scenarios, a zero-length Ping could lead to a client crash, causing a denial of service.
- Discloses gateway WebSocket masking key.
- Malicious peer sends crafted Ping frame.
- Client may crash or leak secrets.
Operational Fix
Recommended remediation, mitigation, and detection steps
This vulnerability in FreeRDP's WebSocket transport requires immediate attention from teams responsible for RDP client deployments and security. The first practical step is to identify all instances of the affected FreeRDP client, determine their network reachability and business criticality, and then assign ownership for remediation. This will involve coordinating with the relevant application or infrastructure teams to plan for applying the fix or implementing temporary mitigations.
- Assign RDP client ownership.
- Verify network exposure and criticality.
- Plan and coordinate remediation.
