[jira] [Comment Edited] (TEXT-42) [XSS] Possible attacks through StringEscapeUtils.escapeEcmaScript?

["Ilguiz Latypov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TEXT-42?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16223929#comment-16223929 ] 

Ilguiz Latypov edited comment on TEXT-42 at 10/29/17 9:56 AM:
--------------------------------------------------------------

I wonder if the escapeEcmaScript()'s use cases can be scrutinized.

* Outputting a standalone javascript file containing string literals.  The generation of string literals to be surrounded by double quotes seems to be covered by the existing code in escapeEcmaScript().  We could extend it to cover cases of   I.e.
{code:java}
String dq = Character.toString('"');
out.println("alert(" + dq + escapeEcmaScript(input) + dq + ");");
{code}
* Outputting an HTML attribute containing javascript containing string literals.  This needs a new method *escapeHtmlAttr*.  Depending on the surrounding quotes or absence of them, all characters of the attribute value will go through either a minimal substitution of [single/double quotes and ampersand|https://html.spec.whatwg.org/multipage/parsing.html#attribute-value-(double-quoted)-state] with the HTML entity or through a broader replacement of [whitespace, ampersand, single/double quotes, equals, greater/less-than and backquotes|https://html.spec.whatwg.org/multipage/parsing.html#attribute-value-(unquoted)-state]. Safety calls to use the broader escaping by default (and allow the narrow one as an option). I.e.
{code:java}
out.println("onmouseover=" + dq + escapeHtmlAttr("alert(" + dq + escapeEcmaScript(input) + dq + ")") + dq);
{code}
* Outputting string literals in the script tag contents. The existing code *lacks protection* against the script's end tag taking precedence over any contents.  Because browsers allow readable javascript between the script tags, browsers [stopped applying a straight decoding algorithm|https://stackoverflow.com/questions/41297404/is-it-possible-to-correctly-escape-arbitrary-script-tag-contents] similar to one in HTML attributes.  The code in escapeEcmaScript() *must escape the less-than character* (with either backslash-x notation or with a simple backslash prefix).  I suggest to escape ampersands (assuming that browsers may keep applying their HTML entity decoding throughout the script tag contents).  Escaping the greater-than character does not seem necessary but would look symmetrical to escaping the less-than character.
{code:java}
out.println("<script>alert(" + dq + escapeEcmaScript(input) + dq + ")</script>");
{code}



was (Author: ilatypov):
I wonder if the escapeEcmaScript()'s use cases can be scrutinized.

* Outputting a standalone javascript file containing string literals.  The generation of string literals to be surrounded by double quotes seems to be covered by the existing code in escapeEcmaScript().  We could extend it to cover cases of   I.e.
{code:java}
String dq = Character.toString('"');
out.println("alert(" + dq + escapeEcmaScript(input) + dq + ");");
{code}
* Outputting an HTML attribute containing javascript containing string literals.  This needs a new method escapeHtmlAttr.  Depending on the surrounding quotes or absence of them, all characters of the attribute value will go through either a minimal substitution of [single/double quotes and ampersand|https://html.spec.whatwg.org/multipage/parsing.html#attribute-value-(double-quoted)-state] with the HTML entity or through a broader replacement of [whitespace, ampersand, single/double quotes, equals, greater/less-than and backquotes|https://html.spec.whatwg.org/multipage/parsing.html#attribute-value-(unquoted)-state]. Safety calls to use the broader escaping by default (and allow the narrow one as an option). I.e.
{code:java}
out.println("onmouseover=" + dq + escapeHtmlAttr("alert(" + dq + escapeEcmaScript(input) + dq + ")") + dq);
{code}
* Outputting string literals in the script tag contents. The existing code *lacks protection* against the script's end tag taking precedence over any contents.  Because browsers allow readable javascript between the script tags, browsers [stopped applying a straight decoding algorithm|https://stackoverflow.com/questions/41297404/is-it-possible-to-correctly-escape-arbitrary-script-tag-contents] similar to one in HTML attributes.  The code in escapeEcmaScript() *must escape the less-than character* (with either backslash-x notation or with a simple backslash prefix).  I suggest to escape ampersands (assuming that browsers may keep applying their HTML entity decoding throughout the script tag contents).  Escaping the greater-than character does not seem necessary but would look symmetrical to escaping the less-than character.
{code:java}
out.println("<script>alert(" + dq + escapeEcmaScript(input) + dq + ")</script>");
{code}


> [XSS] Possible attacks through StringEscapeUtils.escapeEcmaScript?
> ------------------------------------------------------------------
>
>                 Key: TEXT-42
>                 URL: https://issues.apache.org/jira/browse/TEXT-42
>             Project: Commons Text
>          Issue Type: Bug
>            Reporter: Andy Reek
>              Labels: XSS
>             Fix For: 1.x
>
>
> org.apache.commons.lang3.StringEscapeUtils.escapeEcmaScript does the escape via a prefixed '\' on all characters which must be escaped. I am not sure if this is really secure, if am looking at the comments on https://www.owasp.org/index.php/XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet#RULE_.233_-_JavaScript_Escape_Before_Inserting_Untrusted_Data_into_JavaScript_Data_Values. They say it is possible to do an attack by escape the escape. I tested this with the string '\"' and the output was '\\\"'. Is this really ecma-/java-script secure? Or is it better to use the implementation used by OWASP?



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