| Internet-Draft | WebSocket Extension to disable masking | May 2023 |
| Damjanovic | Expires 20 November 2023 | [Page] |
The WebSocket protocol specifies that all frames sent from the client to the server must be masked. This was introduced as a protection against a possible attack on the infrastructure. With careful consideration, the masking could be omitted when intermediaries do not have access to the unencrypted traffic.¶
This specification introduces a WebSocket extension that disables the mandatory masking of frames sent from the client to the server. The extension is allowed only under special circumstances where masking is known to be unnecessary.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
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The WebSocket protocol specifies that all frames sent from the client to the server must be masked [RFC6455]. This was introduced as a protection against a possible attack on the infrastructure described in Section 10.3 of [RFC6455]. The attack can be performed on intermediaries, such as proxies and it could cause cache poisoning. Using end-to-end encryption, the attack can be mitigated without the use of masking. This is because every intermediary will be denied access to the unencrypted traffic, which prevents the caching attack. The masking has been made mandatory for the connection using TLS to protect the infrastructure that is behind TLS terminating proxies.¶
This specification introduces a WebSocket extension that disables the masking of frames sent from the client to the server. The support for the extension will be advertised by the client (see Section 9 of [RFC6455]). The server may accept the extension only after careful consideration discussed in Section Section 3.1. The extension may only be advertised if secure transport is used.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The "no-masking" extension is negotiated using the WebSocket extension mechanism described in Section 9 of [RFC6455]. The client advertises support for the extension by sending "no-masking" in the list of supported extensions sent in the "Sec-WebSocket-Extensions" header field. The server accepts the extension, by sending "no-masking" in the "Sec-WebSocket-Extensions" header value.¶
The client MUST NOT send the extension if a non-secure connection is not used on the connection. The server MUST reject the upgrade request if the "no-masking" extension is advertised on a non-secure connection.¶
If the "no-masking" extension is negotiated the client and the server behavior are:¶
If a WebSocket connection is end-to-end encrypted the server can accept the "no-masking" extension.¶
In case the connection is not end-to-end encrypted MUST NOT accept the "no-masking" extension.¶
Intermediaries that terminate TLS connection should remove the extension from the "Sec-WebSocket-Extensions" header field.¶
IANA has registered the following WebSocket extension name in the "WebSocket Extension Name Registry" defined in [RFC6455].¶
Extension Identifier: no-masking¶
Extension Common Name: Disable the WebSocket client-to-server masking¶
Extension Definition: This document.¶
Known Incompatible Extensions: None¶
The "no-masking" extension name is used in the "Sec-WebSocket-Extensions" header in the WebSocket opening handshake to negotiate disabling of the client-to-server masking.¶