[SLING-8879] Make JSONObject#toString and XSSAPI#encodeForJSString both safe and correct for pasting into a javascript string literal

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: XSS Protection API
• Assignee: Unassigned
• Reporter: Ilguiz Latypov
• Created: 05/Dec/19 15:51
• Updated: 22/Feb/23 08:01

Description

The current implementation risks exceptions in strict javascript engines.

return source == null ? null : Encode.forJavaScript(source).replace("\\-", "\\u002D");

Substitutes on top of the encoder's result with the intent to correct the encoder are near-sighted (i.e. suffer from the context-free approach). If source had a backslash followed by a dash, i.e. raw \-, the forJavaScript call would properly change the backslash into 2 backslashes raw \\- (this would result in the javascript engine turning the string literal back to raw \-). But the subsequent replace call will destroy the context of the second backslash, turning the string into raw \\u002D which would turn to raw \u002D in the javascript engine's variable.

I argue for dropping the .replace() call (aiming at disabling malicious comment injection) here and encoding the opening angle bracket raw < as raw \u003C in the Encode.forJavaScript implementation. This will protect against both the malicious comment injection and the injection of closing script tags raw <\script> forcing the javascript interpreter to drop out of the string literal context and drop out of the script context.

The existing prefixing of forward slashes with a backslash agrees with JSON but not with Javascript. It should be removed in favour of replacing just the opening angle bracket.

SingleEscapeCharacter :: one of
' " \ b f n r t v

https://www.ecma-international.org/ecma-262/6.0/#sec-literals-string-literals

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String#Escape_notation

I noticed that JSONObject#toString suffers from the same idea of a non-universal protection of the forward slash. I guess both XSSAPI and JSONObject#toString reuse the same code.

Issue Links

• fixes: SLING-11768 Display Context "scriptString" encodes hyphen (-) as \u002D
• is caused by: SLING-5946 XSSAPI#encodeForJSString is not restrictive enough