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High

Grav vulnerable to Denial of Service via Improper Input Handling in 'Supported' Parameter

  • Disclosed: 02.12.2025
  • Updated: 11.10.2026 10:22

Endpoint: admin/config/system
Submenu: Languages
Parameter: Supported
Application: Grav v 1.7.48

Summary

A Denial of Service (DoS) vulnerability was identified in the "Languages" submenu of the Grav admin configuration panel (/admin/config/system). Specifically, the Supported parameter fails to properly validate user input. If a malformed value is inserted—such as a single forward slash (/) or an XSS test string—it causes a fatal regular expression parsing error on the server.

This leads to application-wide failure due to the use of the preg_match() function with an improperly constructed regular expression, resulting in the following error:

preg_match(): Unknown modifier 'o' File: /system/src/Grav/Common/Language/Language.php line 244

Once triggered, the site becomes completely unavailable to all users.

Details

  • Vulnerable Endpoint: POST /admin/config/system

  • Submenu: Languages

  • Parameter: Supported

The application dynamically constructs a regular expression using the contents of the Supported field without escaping the input using preg_quote() or proper validation. This allows attackers to inject invalid syntax into the regex engine, crashing the application during language resolution.

Stack trace excerpt:

Whoops \ Exception \ ErrorException (E_WARNING) preg_match(): Unknown modifier 'o' /system/src/Grav/Common/Language/Language.php244

Proof of Concept (PoC)

Payloads:

/

Steps to Reproduce:

  1. Log into the Grav Admin Panel.

  2. Navigate to: Configuration → System → Languages.

  3. Locate the Supported field.

  4. Insert one of the payloads above (e.g., a single slash /).

  5. Click Save.

<img width="1897" height="639" alt="Pasted image 20250719183223" src="https://github.com/user-attachments/assets/d3a54a20-d30d-46c6-9015-722f80701cfb" />
  1. Observe: All pages in the application begin throwing a fatal error and become inaccessible.
<img width="1802" height="998" alt="Pasted image 20250719175229" src="https://github.com/user-attachments/assets/b16750c2-507f-4c30-a9bb-d07fa92bb777" />

Impact

  • Application-wide Denial of Service (DoS)

  • All login and admin views crash with the same error

  • Potentially exploitable by:

    • Admin panel users

    • CSRF if misconfigured

References

  • CWE-1333: Improper Regular Expression

  • CWE-20: Improper Input Validation

Discoverer

Marcelo Queiroz

by CVE-Hunters

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Composer package getgrav/grav < 1.8.0-beta.27 1.8.0-beta.27

References

CVSS score -
CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
Weakness (CWE)
CWE-248
Platform
Composer
Package
getgrav/grav
Disclosed
02.12.2025
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-m8vh-v6r6-w7p6 - CC BY 4.0

Vulnerability history: getgrav/grav

All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (99) in the archive
Total entries
99
First → latest
11.2019 09.2026
Without a fix
6
Exploited in attacks
0

Severity breakdown

  • Critical 7
  • High 47
  • Medium 41
  • Low 4

Disclosures per year

Severity:
  1. Grav vulnerable to Denial of Service via Improper Input Handling in 'Supported' Parameter this entry
    High CVE-2025-66305 < 1.8.0-beta.27 1.8.0-beta.27
  2. Grav CMS vulnerable to remote code execution via .zip file upload
    High · 8.8 CVE-2026-72819 < 2.0.13 2.0.13
  3. Grav: Missing admin.super guard on core group blueprint access field allows admin.users operator to escalate to super-admin
    High · 9.1 CVE-2026-75837 < 2.0.14 2.0.14
  4. Grav: Blueprint dynamic-data bare-function branch is denylist-gated and omits error_log, giving arbitrary file write
    Critical · 8.8 CVE-2026-75827 < 2.0.15 2.0.15
  5. Grav: detectXss() misses an event-handler attribute after an unpaired quote in an unquoted attribute value, giving stored XSS
    Critical · 8.7 CVE-2026-75828 < 2.0.15 2.0.15
  6. Grav: Unauthenticated Path Traversal via Missing Directory-Boundary Check in `plugin-asset-map.php` Static Asset Server (`index.php`)
    High · 5.9 CVE-2026-74907 < 2.0.15 2.0.15
  7. Grav: Path Traversal in MediaUploadTrait::deleteFile() Allows Arbitrary File Deletion
    High · 8.1 CVE-2026-72695 < 2.0.16 2.0.16
  8. Grav: media_directory() Twig function allows filesystem path traversal and file content disclosure from sandboxed page content
    High · 6.5 CVE-2026-72697 < 2.0.16 2.0.16
  9. Grav: UserInterface offsetget/offsetexists allow-listed in Twig sandbox let editor-authored content leak hashed_password and 2FA secrets via offsetGet()
    High · 7.7 CVE-2026-76839 < 2.0.16 2.0.16
  10. Grav: config_denied_paths default list omits `system`, exposing real secrets (e.g. system.cache.redis.password) via the Twig sandbox when config_access is enabled
    High · 7.5 CVE-2026-76846 < 2.0.16 2.0.16
  11. Grav: The system, site, and theme Twig variables bypass the content sandbox entirely and are never covered by config_denied_paths
    High · 6.5 CVE-2026-72698 < 2.0.16 2.0.16
  12. Grav: Path Traversal in ImageMedium::watermark() — arbitrary file disclosure via publicly-cached images
    High CVE-2026-69089 >= 2.0.10, < 2.0.11 2.0.11
  13. Grav: Incomplete callable validation in blueprint dynamic fields allows arbitrary static method invocation and file disclosure
    High · 8.1 CVE-2026-69088 >= 2.0.7, < 2.0.11 2.0.11
  14. Grav: FlexDirectory::dynamicDataField() executes arbitrary callables from blueprint data with no validation
    High · 8.8 CVE-2026-65608 >= 1.7.0, < 2.0.9 2.0.9
  15. Grav: 2FA Bypass via 'login.regenerate2FASecret' - Secret Rotation During Pending Challenge
    High · 7.4 CVE-2026-62232 < 2.0.4 2.0.4
  16. Grav: Remote code execution via unrestricted callable in Blueprint::dynamicData()
    High CVE-2026-64850 < 2.0.7 2.0.7
  17. Grav: .htaccess file extension rules bypass via case variation on case-insensitive filesystems
    High CVE-2026-62230 < 2.0.4 2.0.4
  18. Grav: Unauthenticated denial of service via unbounded image derivative dimensions
    High CVE-2026-53653 >= 2.0.0-beta.1, < 2.0.0-rc.8, < 1.7.53 2.0.0-rc.8, 1.7.53
  19. Grav: Twig sandbox allows editor-role users to exfiltrate all plugin secrets via Config::toArray()
    High · 7.7 CVE-2026-44738 < 2.0.0-rc.2 2.0.0-rc.2
  20. Low-privileged Grav API users can create super-admin accounts via blueprint-upload
    High CVE-2026-42844 < 2.0.0-beta.4 2.0.0-beta.4
  21. Grav is Vulnerable to Stored XSS via Tag Injection
    High · 8.9 CVE-2026-42611 < 2.0.0-beta.2 2.0.0-beta.2
Show more (20) Showing 21 of 54

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