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Harden archive extraction: zip-slip protection + exit-code error handling #147

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Harden archive extraction: zip-slip protection + exit-code error handling #147

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c5e558b
fix(security): reject archive entries with traversal or absolute paths
kaibae19 May 21, 2026
44d3943
fix: use exit codes (not stdout line counts) to detect tool failure
kaibae19 May 21, 2026
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122 changes: 115 additions & 7 deletions lib/Service/ExtractionService.php
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,90 @@ public function __construct(
) {
}

/**
* Reject absolute paths and any ".." path component. Modern libzip
* blocks traversal in ZipArchive::extractTo, but neither unrar nor
* 7za do — a crafted archive can write outside $extractTo.
*/
private function isUnsafePath(string $entry): bool {
$norm = str_replace('\\', '/', $entry);
if ($norm === '' || $norm === '.' || $norm === './') {
return false;
}
if (str_starts_with($norm, '/')) {
return true;
}
return (bool)preg_match('#(^|/)\.\.($|/)#', $norm);
}

/** @return null|array{code: 0, desc: string} */
private function rejectUnsafe(string $entry): ?array {
if (!$this->isUnsafePath($entry)) {
return null;
}
$this->logger->warning('Refusing archive with unsafe entry: ' . $entry);
return [
'code' => 0,
'desc' => $this->l->t('Archive contains an unsafe path and was not extracted'),
];
}

/** Validate every ZIP entry via libzip indices. @return null|array{code: 0, desc: string} */
private function assertSafeZip(ZipArchive $zip): ?array {
for ($i = 0; $i < $zip->numFiles; $i++) {
$name = $zip->getNameIndex($i);
if ($name === false) {
return ['code' => 0, 'desc' => $this->l->t('Failed to read archive index')];
}
if ($err = $this->rejectUnsafe($name)) {
return $err;
}
}
return null;
}

/** Validate every RAR entry via `unrar lb` (bare list). @return null|array{code: 0, desc: string} */
private function assertSafeRarShell(string $file): ?array {
$output = [];
$return = 0;
exec('unrar lb ' . escapeshellarg($file) . ' 2>&1', $output, $return);
if ($return !== 0) {
$this->logger->error('unrar list failed (rc=' . $return . '): ' . implode("\n", $output));
return ['code' => 0, 'desc' => $this->l->t('Failed to inspect RAR contents')];
}
foreach ($output as $line) {
$line = trim($line);
if ($line === '') {
continue;
}
if ($err = $this->rejectUnsafe($line)) {
return $err;
}
}
return null;
}

/** Validate every entry via `7za l -ba -slt`. @return null|array{code: 0, desc: string} */
private function assertSafe7z(string $file): ?array {
$output = [];
$return = 0;
exec('7za l -ba -slt ' . escapeshellarg($file) . ' 2>&1', $output, $return);
if ($return !== 0) {
$this->logger->error('7za list failed (rc=' . $return . '): ' . implode("\n", $output));
return ['code' => 0, 'desc' => $this->l->t('Failed to inspect archive contents')];
}
foreach ($output as $line) {
if (!str_starts_with($line, 'Path = ')) {
continue;
}
$entry = substr($line, 7);
if ($err = $this->rejectUnsafe($entry)) {
return $err;
}
}
return null;
}

/**
* @return (bool|int|mixed)[]
*
Expand All @@ -40,6 +124,11 @@ public function extractZip(string $file, string $extractTo): array {
return $response;
}

if ($err = $this->assertSafeZip($zip)) {
$zip->close();
return $err;
}

$success = $zip->extractTo($extractTo);
$zip->close();
$response = array_merge($response, ['code' => $success ? 1 : 0]);
Expand All @@ -55,14 +144,27 @@ public function extractRar(string $file, string $extractTo): array {
$response = [];

if (!extension_loaded('rar')) {
exec('unrar x ' . escapeshellarg($file) . ' -R ' . escapeshellarg($extractTo) . '/ -o+', $output, $return);
if (sizeof($output) <= 4) {
$response = array_merge($response, ['code' => 0, 'desc' => $this->l->t('Oops something went wrong. Check that you have rar extension or unrar installed')]);
if ($err = $this->assertSafeRarShell($file)) {
return $err;
}
$output = [];
$return = 0;
exec('unrar x ' . escapeshellarg($file) . ' -R ' . escapeshellarg($extractTo) . '/ -o+ 2>&1', $output, $return);
if ($return !== 0) {
$this->logger->error('unrar extract failed (rc=' . $return . '): ' . implode("\n", $output));
$response = array_merge($response, ['code' => 0, 'desc' => $this->l->t('Failed to extract RAR archive (is the rar extension or unrar installed?)')]);
return $response;
}
} else {
$rar_file = rar_open($file);
$list = rar_list($rar_file);
// Pre-validate every entry before extracting any of them.
foreach ($list as $archive_file) {
if ($err = $this->rejectUnsafe($archive_file->getName())) {
rar_close($rar_file);
return $err;
}
}
foreach ($list as $archive_file) {
$entry = rar_entry_get($rar_file, $archive_file->getName());
$entry->extract($extractTo);
Expand All @@ -82,11 +184,17 @@ public function extractRar(string $file, string $extractTo): array {
public function extractOther(string $file, string $extractTo): array {
$response = [];

exec('7za -y x ' . escapeshellarg($file) . ' -o' . escapeshellarg($extractTo), $output, $return);
if ($err = $this->assertSafe7z($file)) {
return $err;
}

$output = [];
$return = 0;
exec('7za -y x ' . escapeshellarg($file) . ' -o' . escapeshellarg($extractTo) . ' 2>&1', $output, $return);

if (sizeof($output) <= 5) {
$response = array_merge($response, ['code' => 0, 'desc' => $this->l->t('Oops something went wrong.')]);
$this->logger->error('Is 7-Zip installed? Output: ' . print_r($output, true));
if ($return !== 0) {
$this->logger->error('7za extract failed (rc=' . $return . '): ' . implode("\n", $output));
$response = array_merge($response, ['code' => 0, 'desc' => $this->l->t('Failed to extract archive (is 7-Zip installed?)')]);
return $response;
}
$response = array_merge($response, ['code' => 1]);
Expand Down