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Posted to dev@sling.apache.org by "Ilguiz Latypov (Jira)" <ji...@apache.org> on 2019/12/04 23:27:00 UTC
[jira] [Comment Edited] (SLING-5946) XSSAPI#encodeForJSString is
not restrictive enough
[ https://issues.apache.org/jira/browse/SLING-5946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16988288#comment-16988288 ]
Ilguiz Latypov edited comment on SLING-5946 at 12/4/19 11:26 PM:
-----------------------------------------------------------------
Please reopen this due to an improper implementation risking 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 {{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 here and encoding the opening angle bracket {{raw <}} as {{raw \u003C}} in the {{Encode.forJavaScript}} implementation. This will also protect against the 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.
{noformat}
SingleEscapeCharacter :: one of
' " \ b f n r t v
{noformat}
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
was (Author: ilatypov):
Please reopen this due to an improper implementation risking 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 {{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 here and encoding the opening angle bracket {{raw <}} as {{raw \u003C}} in the Encode.forJavaScript() implementation. This will also protect against the 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.
> XSSAPI#encodeForJSString is not restrictive enough
> --------------------------------------------------
>
> Key: SLING-5946
> URL: https://issues.apache.org/jira/browse/SLING-5946
> Project: Sling
> Issue Type: Bug
> Components: Extensions
> Affects Versions: XSS Protection API 1.0.8
> Reporter: Vlad Bailescu
> Assignee: Robert Munteanu
> Priority: Major
> Fix For: XSS Protection API 1.0.12
>
> Attachments: SLING_5946.patch
>
>
> Since SLING-5445, {{XSSAPI#encodeForJSString}} is no longer properly encoding {{</script>}} and {{<!--}}. We should revert to using OWASP {{Encode#forJavaScript}} and handle - characters correctly for JSON too, by replacing them with {{\u002D}}
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