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https://issues.apache.org/jira/browse/LUCENE-7256?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Adrien Grand updated LUCENE-7256:
---------------------------------
Priority: Minor (was: Critical)
> PatternReplaceCharFilter can make Lucene hang
> ---------------------------------------------
>
> Key: LUCENE-7256
> URL: https://issues.apache.org/jira/browse/LUCENE-7256
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/analysis
> Affects Versions: 5.4.1
> Environment: alpine linux v3.3
> Reporter: Tom Fotherby
> Priority: Minor
>
> I'm using ElasticSearch (v2.2.0 , Lucene v5.4.1) and it's [Pattern Replace
> Char
> Filter|https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-pattern-replace-charfilter.html]
> (Lucenes PatternReplaceCharFilter) . I need to filter out urls from my query
> text before it is tokenised. But I found that some input strings cause
> ElasticSearch to "hang" (slowly eating more CPU and memory) until the system
> crashes.
> ----
> *Example*
> {code}
> // Character filters are used to "tidy up" a string *before* it is tokenized.
> 'char_filter' => [
> 'url_removal_pattern' => [
> 'type' => 'pattern_replace',
> 'pattern' =>
> '(?mi)\b((?:[a-z][\w-]+:(?:\/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}\/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:\'".,<>?«»""'']))',
> 'replacement' => '',
> ],
> {code}
> This filter was working fine for some weeks until suddenly ElasticSearch
> started crashing. We found someone was trying to do a javascript injection
> attack in our search box.
> I pasted the regex and the attack string into https://regex101.com
> * Regexp:
> *
> {code}(?mi)\b((?:[a-z][\w-]+:(?:\/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}\/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s!()\[\]{};:\'".,<>?«»""''])){code}
> * Test string:
> *
> {code}twitter.com/widgets.js\";fjs.parentNode.insertBefore(js,fjs);}}(document,\"script\",\"twitter-wjs\"{code}
> https://regex101.com shows the problem to be "Catastrophic backtracking"
> bq. Catastrophic backtracking has been detected and the execution of your
> expression has been halted. To find out more what this is, please read the
> following article: [Runaway Regular
> Expressions|http://www.regular-expressions.info/catastrophic.html].
> It would be great if Lucene could detect "Catastrophic backtracking" and
> throw a error or return null.
> ----
> As an aside, I created a unit test for our PHP application that uses the same
> regexp and test string. (PHP can understand the same regexp, even though it's
> obviously for Java in the ElasticSearch case) . Interestingly in php, the
> regex results in `null` which is the documented response of
> [preg_replace|http://php.net/manual/en/function.preg-replace.php] when a
> error occurs. If PHP can return a error rather than crashing - surely Lucene
> / Java can too :trollface: ?
> {code}
> namespace app\tests\unit;
> use \yii\codeception\TestCase;
> class TagsControllerTest extends TestCase
> {
> public function testRegexForURLDetection()
> {
> $regex =
> '(?mi)\b((?:[a-z][\w-]+:(?:\/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}\/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:\'".,<>?«»""'']))';
> // Test the Catastrophic backtracking problem
> $testString =
> "twitter.com/widgets.js\";fjs.parentNode.insertBefore(js,fjs);}}(document,\"script\",\"twitter-wjs\"";
> // This shows the regex is not working for our test string - it gives
> null but should give 'hello '
> $this->assertEquals(null, preg_replace("/$regex/", '', "hello
> $testString"));
> }
> }
> {code}
> ----
> (I originally [opened a
> ticket|https://github.com/elastic/elasticsearch/issues/17934] to the
> ElasticSearch project but got told opening it here would be more appropriate
> - sorry if I'm wrong)
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