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From "Bruce Brouwer (JIRA)" <j...@apache.org>
Subject [jira] [Closed] (LOG4J2-439) Create a LogEventPatternConverter to escape newlines and HTML special characters
Date Sun, 04 May 2014 13:57:14 GMT

     [ https://issues.apache.org/jira/browse/LOG4J2-439?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Bruce Brouwer closed LOG4J2-439.
--------------------------------


> Create a LogEventPatternConverter to escape newlines and HTML special characters
> --------------------------------------------------------------------------------
>
>                 Key: LOG4J2-439
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-439
>             Project: Log4j 2
>          Issue Type: New Feature
>          Components: Layouts
>    Affects Versions: 2.0-beta9
>            Reporter: Bruce Brouwer
>            Assignee: Ralph Goers
>             Fix For: 2.0-rc2
>
>         Attachments: EncodingPatternConverter.patch, log4j2-439-doc.patch
>
>
> To prevent log forging and HTML based attacks from viewing logs in a browser, we could
add a LogEventPatternConverter that escapes newlines and HTML special characters. [ESAPI has
a method to do this|http://owasp-esapi-java.googlecode.com/svn/trunk_doc/2.0-rc7/apidocs/org/owasp/esapi/Logger.html],
but it doesn't have any of the nice API features that Log4j 2 has. 
> I was able to create a LogEventPatternConverter to do this. Note, this is only a proof
of concept. I didn't try to exhaustively list all the special characters that might need to
be replaced. I also didn't provide any configuration so we could choose to not escape HTML,
for example.
> With this configuration:
> {code:xml}
> <PatternLayout pattern="%d %-5p [%t] %c %encode{%m}%n"/>
> {code}
> And logging this message:
> {code}
> LOG.warn("hi\n & <h1> there");
> {code}
> Would result in this being logged:
> {code}
> 2013-10-28 16:31:21,606 WARN  [main] example.Test hi\n &amp; &lt;h1&gt; there

> {code}
> instead of this (which shows the potential for log forging):
> {code}
> 2013-10-28 16:31:21,606 WARN  [main] example.Test hi
> & <h1> there 
> {code}
> This is roughly the code I used:
> {code}
> @Plugin(name = "escape", category = "Converter")
> @ConverterKeys({ "escape" })
> public final class EscapingReplacementConverter extends LogEventPatternConverter {
>     private final List<PatternFormatter> formatters;
>     private EscapingReplacementConverter(final List<PatternFormatter> formatters)
{
>         super("escape", "escape");
>         this.formatters = formatters;
>     }
>     public static EscapingReplacementConverter newInstance(final Configuration config,
>                                                            final String[] options) {
>         if (options.length != 1) {
>             LOGGER.error("Incorrect number of options on escape. Expected 1, received
"
>                     + options.length);
>             return null;
>         }
>         if (options[0] == null) {
>             LOGGER.error("No pattern supplied on escape");
>             return null;
>         }
>         final PatternParser parser = PatternLayout.createPatternParser(config);
>         final List<PatternFormatter> formatters = parser.parse(options[0]);
>         return new EscapingReplacementConverter(formatters);
>     }
>     @Override
>     public void format(final LogEvent event, final StringBuilder toAppendTo) {
>         final StringBuilder buf = new StringBuilder();
>         for (final PatternFormatter formatter : formatters) {
>             formatter.format(event, buf);
>         }
>         toAppendTo.append(buf.toString()
>                              .replaceAll("\\r", "\\\\r")
>                              .replaceAll("\\n", "\\\\n")
>                              .replaceAll("&", "&amp;")
>                              .replaceAll("<", "&lt;")
>                              .replaceAll(">", "&gt;"));
>     }
> }
> {code}
> If this sounds good, I would like to hear feedback and ideas on how to make this better.
I will then contribute this to the project. Do you think this could this get in 2.0?



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