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security: replace vulnerable regex with parser #1223

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Merged
merged 5 commits into from
Apr 17, 2018
Merged

security: replace vulnerable regex with parser #1223

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4717be9
security: replace vulnerable regex with parser
davisjam Apr 15, 2018
1ad9ca0
Travis failure: use backwards-compatible JS
davisjam Apr 15, 2018
fbf93a8
address review comments
davisjam Apr 16, 2018
ba2fc13
address review comments
davisjam Apr 16, 2018
47f4388
address review comments
davisjam Apr 16, 2018
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69 changes: 66 additions & 3 deletions lib/marked.js
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Original file line number Diff line number Diff line change
Expand Up @@ -554,9 +554,72 @@ inline.normal = merge({}, inline);
inline.pedantic = merge({}, inline.normal, {
strong: /^__(?=\S)([\s\S]*?\S)__(?!_)|^\*\*(?=\S)([\s\S]*?\S)\*\*(?!\*)/,
em: /^_(?=\S)([\s\S]*?\S)_(?!_)|^\*(?=\S)([\s\S]*?\S)\*(?!\*)/,
link: edit(/^!?\[(label)\]\(\s*<?([\s\S]*?)>?(?:\s+(['"][\s\S]*?['"]))?\s*\)/)
.replace('label', inline._label)
.getRegex(),
/* Original link re: /^!?\[(label)\]\(\s*<?([\s\S]*?)>?(?:\s+(['"][\s\S]*?['"]))?\s*\)/
* This captures the spec reasonably well but is vulnerable to REDOS.
* Instead we use a custom parser that follows the RegExp.exec semantics. */
link: {
exec: function (s) {
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@joshbruce joshbruce Apr 16, 2018 •
edited
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Might be worth adding some doc blocks to introduce the why behind some of this...nothing too major, just to help those new to the code.

// [TEXT](DESTINATION)
var generalLinkRe = edit(/^!?\[(label)\]\((.*?)\)/)
.replace('label', inline._label)
.getRegex();

// destination: DESTINATION from generalLinkRe
// returns [destination, title]: no angle-brackets on destination, no quotes on title
function splitIntoDestinationAndTitle (destination) {
function unwrapAngleBrackets (str) {
if (str.match(/^<.*>$/)) {
str = str.slice(1, -1);
}
return str;
}

// Valid DESTINATIONs, in decreasing specificity.
var destinationAndTitleRe = /^([^'"(]*[^\s])\s+(['"(].*['")])/;
var destinationRe = /^(<?[\s\S]*>?)/;
var parsingRegexes = [destinationAndTitleRe, destinationRe];

var match = false;
var dest = undefined;
var title = undefined;
for (var i = 0; i < parsingRegexes.length; i++) {
match = parsingRegexes[i].exec(destination);
if (match) {
dest = match[1];
title = match[2];
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@styfle styfle Apr 16, 2018

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You don't need to assign dest and title here. Simply use match below.

break;
}
}

if (match) {
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@styfle styfle Apr 16, 2018 •
edited
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Can you flip this so that the if statement is smaller:

if (!match) {
  return null;
}
// ... get dest and title here
return [dest, title];

// title is optional.
if (typeof title === 'undefined') {
title = '';
}

// Format dest.
dest = dest.trim();
dest = unwrapAngleBrackets(dest);

return [dest, title];
}
return null;
}

var fullMatch = generalLinkRe.exec(s);
if (fullMatch) {
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@styfle styfle Apr 16, 2018

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Can you flip this so that the if statement is smaller:

if (!fullMatch) {
  return null;
}
// ... split and such here
return [fullMatch[0], text, destinationAndTitle[0], destinationAndTitle[1]];

var text = fullMatch[1];
var destination = fullMatch[2];

// Does 'destination' match spec?
var destinationAndTitle = splitIntoDestinationAndTitle(destination);
if (destinationAndTitle) {
return [fullMatch[0], text, destinationAndTitle[0], destinationAndTitle[1]];
}
}
return null;
}
},
reflink: edit(/^!?\[(label)\]\s*\[([^\]]*)\]/)
.replace('label', inline._label)
.getRegex()
Expand Down