CVE-2023-34253

Grav is a flat-file content management system. Prior to version 1.7.42, the denylist introduced in commit 9d6a2d to prevent dangerous functions from being executed via injection of malicious templates was insufficient and could be easily subverted in multiple ways -- (1) using unsafe functions that are not banned, (2) using capitalised callable names, and (3) using fully-qualified names for referencing callables. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution. A patch in version 1.7.42 improves the denylist.

Grav is a flat-file content management system. Prior to version 1.7.42, the denylist introduced in commit 9d6a2d to prevent dangerous functions from being executed via injection of malicious templates was insufficient and could be easily subverted in multiple ways -- (1) using unsafe functions that are not banned, (2) using capitalised callable names, and (3) using fully-qualified names for referencing callables. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution. A patch in version 1.7.42 improves the denylist.

Hi,

actually we have sent the bug report to [email protected] on 27th March 2023 and on 10th April 2023.

Grav Server-side Template Injection (SSTI) via Denylist Bypass Vulnerability

Summary:

| Product | Grav CMS | | ----------------------- | --------------------------------------------- | | Vendor | Grav | | Severity | High - Users with login access to Grav Admin panel and page creation/update permissions are able to obtain remote code/command execution | | Affected Versions | <= v1.7.40 (Commit 685d762) (Latest version as of writing) | | Tested Versions | v1.7.40 | | Internal Identifier | STAR-2023-0006 | | CVE Identifier | Reserved CVE-2023-30592, CVE-2023-30593, CVE-2023-30594 | | CWE(s) | CWE-184: Incomplete List of Disallowed Inputs, CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine |

CVSS3.1 Scoring System:

Base Score: 7.2 (High)
Vector String: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
| Metric | Value | | ---------------------------- | --------- | | Attack Vector (AV) | Network | | Attack Complexity (AC) | Low | | Privileges Required (PR) | High | | User Interaction (UI) | None | | Scope (S) | Unchanged | | Confidentiality (C) | High | | Integrity (I) | High | | Availability (A) | High |

Product Overview:

Grav is a PHP-based flat-file content management system (CMS) designed to provide a fast and simple way to build websites. It supports rendering of web pages written in Markdown and Twig expressions, and provides an administration panel to manage the entire website via an optional Admin plugin.

Vulnerability Summary:

The denylist introduced in commit 9d6a2d to prevent dangerous functions from being executed via injection of malicious templates was insufficient and could be easily subverted in multiple ways -- (1) using unsafe functions that are not banned, (2) using capitalised callable names, and (3) using fully-qualified names for referencing callables. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution.

Vulnerability Details:

In addressing CVE-2022-2073, a denylist was introduced in commit 9d6a2d to validate and ensure that dangerous functions could not be executed via injection of malicious templates.

The implementation of the denylist can be found in Utils::isDangerousFunction() within /system/src/Grav/Common/Utils.php:

    /**
     * @param string $name
     * @return bool
     */
    public static function isDangerousFunction(string $name): bool
    {
        static $commandExecutionFunctions = [
            'exec',
            'passthru',
            'system',
            'shell_exec',
            'popen',
            'proc_open',
            'pcntl_exec',
        ];

        static $codeExecutionFunctions = [
            'assert',
            'preg_replace',
            'create_function',
            'include',
            'include_once',
            'require',
            'require_once'
        ];

        static…

Grav is a flat-file content management system. Prior to version 1.7.42, the denylist introduced in commit 9d6a2d to prevent dangerous functions from being executed via injection of malicious templates was insufficient and could be easily subverted in multiple ways -- (1) using unsafe functions that are not banned, (2) using capitalised callable names, and (3) using fully-qualified names for referencing callables. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution. A patch in version 1.7.42 improves the denylist.

Grav is a flat-file content management system. Prior to version 1.7.42, the denylist introduced in commit 9d6a2d to prevent dangerous functions from being executed via injection of malicious templates was insufficient and could be easily subverted in multiple ways -- (1) using unsafe functions that are not banned, (2) using capitalised callable names, and (3) using fully-qualified names for referencing callables. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution. A patch in version 1.7.42 improves the denylist.

Hi,

actually we have sent the bug report to [email protected] on 27th March 2023 and on 10th April 2023.

Grav Server-side Template Injection (SSTI) via Denylist Bypass Vulnerability

Summary:

| Product | Grav CMS | | ----------------------- | --------------------------------------------- | | Vendor | Grav | | Severity | High - Users with login access to Grav Admin panel and page creation/update permissions are able to obtain remote code/command execution | | Affected Versions | <= v1.7.40 (Commit 685d762) (Latest version as of writing) | | Tested Versions | v1.7.40 | | Internal Identifier | STAR-2023-0006 | | CVE Identifier | Reserved CVE-2023-30592, CVE-2023-30593, CVE-2023-30594 | | CWE(s) | CWE-184: Incomplete List of Disallowed Inputs, CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine |

CVSS3.1 Scoring System:

Base Score: 7.2 (High)
Vector String: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
| Metric | Value | | ---------------------------- | --------- | | Attack Vector (AV) | Network | | Attack Complexity (AC) | Low | | Privileges Required (PR) | High | | User Interaction (UI) | None | | Scope (S) | Unchanged | | Confidentiality (C) | High | | Integrity (I) | High | | Availability (A) | High |

Product Overview:

Grav is a PHP-based flat-file content management system (CMS) designed to provide a fast and simple way to build websites. It supports rendering of web pages written in Markdown and Twig expressions, and provides an administration panel to manage the entire website via an optional Admin plugin.

Vulnerability Summary:

The denylist introduced in commit 9d6a2d to prevent dangerous functions from being executed via injection of malicious templates was insufficient and could be easily subverted in multiple ways -- (1) using unsafe functions that are not banned, (2) using capitalised callable names, and (3) using fully-qualified names for referencing callables. Consequently, a low privileged attacker with login access to Grav Admin panel and page creation/update permissions is able to inject malicious templates to obtain remote code execution.

Vulnerability Details:

In addressing CVE-2022-2073, a denylist was introduced in commit 9d6a2d to validate and ensure that dangerous functions could not be executed via injection of malicious templates.

The implementation of the denylist can be found in Utils::isDangerousFunction() within /system/src/Grav/Common/Utils.php:

    /**
     * @param string $name
     * @return bool
     */
    public static function isDangerousFunction(string $name): bool
    {
        static $commandExecutionFunctions = [
            'exec',
            'passthru',
            'system',
            'shell_exec',
            'popen',
            'proc_open',
            'pcntl_exec',
        ];

        static $codeExecutionFunctions = [
            'assert',
            'preg_replace',
            'create_function',
            'include',
            'include_once',
            'require',
            'require_once'
        ];

        static…