CVE-2026-16632 in facil.io
Summary
by MITRE • 07/23/2026
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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Analysis
by VulDB Data Team • 07/23/2026
The vulnerability identified in facil.io version 0.7.4 represents a critical input validation flaw within the WebSocket frame parser component that could enable remote code execution or denial of service attacks. This issue resides in the websocket_on_protocol_error function located in lib/facil/http/parsers/websocket_parser.h, where improper handling of malformed WebSocket frames can lead to arbitrary memory manipulation through the on_message argument. The vulnerability stems from insufficient validation of incoming WebSocket protocol data, allowing attackers to craft malicious frames that exploit buffer handling mechanisms within the parser.
The technical exploitation of this flaw occurs when remote attackers send specially crafted WebSocket frames that trigger the websocket_on_protocol_error function. The improper input validation allows manipulation of the on_message callback parameter, potentially leading to stack-based buffer overflows or heap corruption depending on how the library handles the malformed data. This vulnerability is particularly dangerous because it operates at the protocol parsing layer where all incoming WebSocket traffic must pass through before being processed by application logic, making it an ideal attack vector for compromising the entire application server.
From an operational perspective, this vulnerability presents significant risk to applications using facil.io versions up to 0.7.4 as it enables remote attackers to potentially execute arbitrary code on the affected system or cause service disruption through denial of service conditions. The fact that a working exploit has been published increases the likelihood of real-world exploitation, particularly given the library's use in web applications and microservices architectures where WebSocket communication is common. The vulnerability affects any application that relies on facil.io's WebSocket implementation for real-time communication features.
Security mitigations for this vulnerability include immediate upgrade to version 0.7.5 or later where the parsing logic has been corrected to properly validate incoming WebSocket frames and sanitize input parameters before processing. Organizations should also implement network-level controls such as websocket frame filtering and rate limiting to reduce attack surface while waiting for patches. Additionally, monitoring for unusual WebSocket traffic patterns and implementing proper input validation at application layers can help detect exploitation attempts. This vulnerability aligns with CWE-121 Heap-based Buffer Overflow and CWE-20 Improper Input Validation categories, and represents a technique commonly used in the attack phase of the kill chain as outlined in MITRE ATT&CK framework under T1190 Exploit Public-Facing Application and T1059 Command and Scripting Interpreter. The lack of response from the project maintainers after initial reporting suggests potential delay in patch deployment, emphasizing the need for proactive security measures and alternative mitigation strategies.