CVE-2026-16632
Received Received - Intake

Improper Input Validation in facil.io WebSocket Parser

Publication date: 2026-07-23

Last updated on: 2026-07-23

Assigner: VulDB

Description
A flaw has been found in boazsegev facil.io up to 0.7.4. Affected is the function websocket_on_protocol_error in the library lib/facil/http/parsers/websocket_parser.h of the component WebSocket Frame Parser. This manipulation of the argument on_message causes improper input validation. The attack can be initiated remotely. The exploit has been published and may be used. The project was informed of the problem early through an issue report but has not responded yet.

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Meta Information

Published
2026-07-23
Last Modified
2026-07-23
Generated
2026-07-23
AI Q&A
2026-07-23
EPSS Evaluated
N/A
NVD
CVE-2026-16632
EUVD
EUVD-2026-47864

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
boazsegev facil.io to 0.7.4 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-20 The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

Attack-Flow Graph

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Executive Summary

This vulnerability is a WebSocket protocol validation bypass in facil.io's WebSocket frame parser. A remote attacker can send an invalid client-to-server WebSocket frame with the MASK bit cleared. The server processes the invalid frame and delivers the payload to the application's on_message callback before closing the connection. This allows one unauthorized action per connection using frames that should have been rejected immediately.

Detection Guidance

To detect this vulnerability, monitor WebSocket traffic for frames with the MASK bit cleared from client to server. Check facil.io logs for protocol errors where invalid frames are processed before connection closure. Use network sniffing tools like tcpdump or Wireshark to capture and inspect WebSocket frames for violations of RFC 6455.

Impact Analysis

An attacker could trigger unexpected application actions, alter system state, or cause noisy writes and queue growth. Since the payload is delivered before validation, it may bypass security checks and execute unintended business logic. Each vulnerable connection allows one such action before the server terminates it.

Compliance Impact

This vulnerability could lead to unauthorized data access or modification, violating GDPR's integrity and confidentiality principles or HIPAA's security requirements for protected health information. Unintended state changes or payload processing may result in non-compliance with data protection controls.

Mitigation Strategies

Immediately upgrade facil.io to a patched version if available. If not, implement strict input validation to reject unmasked client frames at the network level before they reach the WebSocket parser. Temporarily disable WebSocket functionality if possible or restrict access to trusted clients only.

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