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Improve DNS response parser to limit recursion for compressed labels #169

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Merged
jsor merged 1 commit into from
Sep 27, 2020
Merged

Improve DNS response parser to limit recursion for compressed labels #169

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12 changes: 9 additions & 3 deletions src/Protocol/Parser.php
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Original file line number Diff line number Diff line change
Expand Up @@ -301,7 +301,13 @@ function ($label) {
);
}

private function readLabels($data, $consumed)
/**
* @param string $data
* @param int $consumed
* @param int $compressionDepth maximum depth for compressed labels to avoid unreasonable recursion
* @return array
*/
private function readLabels($data, $consumed, $compressionDepth = 127)
{
$labels = array();

Expand All @@ -319,14 +325,14 @@ private function readLabels($data, $consumed)
}

// first two bits set? this is a compressed label (14 bit pointer offset)
if (($length & 0xc0) === 0xc0 && isset($data[$consumed + 1])) {
if (($length & 0xc0) === 0xc0 && isset($data[$consumed + 1]) && $compressionDepth) {
$offset = ($length & ~0xc0) << 8 | \ord($data[$consumed + 1]);
if ($offset >= $consumed) {
return array(null, null);
}

$consumed += 2;
list($newLabels) = $this->readLabels($data, $offset);
list($newLabels) = $this->readLabels($data, $offset, $compressionDepth - 1);

if ($newLabels === null) {
return array(null, null);
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12 changes: 12 additions & 0 deletions tests/Protocol/ParserTest.php
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Original file line number Diff line number Diff line change
Expand Up @@ -811,6 +811,18 @@ public function testParseInvalidOffsetPointerToSameLabelInQuestionNameThrows()
$this->parser->parseMessage($data);
}

public function testParseInvalidOffsetPointerToPreviousLabelInQuestionNameThrows()
{
$data = "";
$data .= "72 62 01 00 00 01 00 00 00 00 00 00"; // header
$data .= "02 69 6f c0 0c"; // question: offset pointer to previous label

$data = $this->convertTcpDumpToBinary($data);

$this->setExpectedException('InvalidArgumentException');
$this->parser->parseMessage($data);
}

public function testParseInvalidOffsetPointerToStartOfMessageInQuestionNameThrows()
{
$data = "";
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