CVE-2021-29440: Getgrav/grav Grav's Twig Processing Allowing Dangerous Vulnerability

HIGH
Advisory Identifier: GHSA-g8r4-p96j-xfxc
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CVSS 8.4
CWE-94
Published
Advisory Summary

CVE-2021-29440 is a HIGH (CVSS 8.4) grav's twig processing allowing dangerous vulnerability (CWE-94: Improper Control of Generation of Code ('Code Injection')) affecting Getgrav/grav libraries in the Packagist ecosystem. The issue involves grav's twig processing allowing dangerous php functions by default. Remediation is available by upgrading affected packages to version 1.7.11.

CVE-2021-29440 at a Glance

CVE Identifier CVE-2021-29440
GHSA Identifier GHSA-g8r4-p96j-xfxc
Severity HIGH
CVSS v3.1 Base Score 8.4
CWE Classification CWE-94: Improper Control of Generation of Code ('Code Injection')
Affected Product Getgrav/grav
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 8.4

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required High (PR:H)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2021-29440

To remediate this vulnerability, upgrade all affected Getgrav/grav dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

getgrav/grav fixed: 1.7.11 
Upgrade getgrav/grav to 1.7.11
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for getgrav/grav

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-29440, inspect your project dependencies for Getgrav/grav:

inspect dependencies for getgrav/grav

Analyze the terminal output to locate any version of Getgrav/grav in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.7.11), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-94: Improper Control of Generation of Code ('Code Injection'), where the product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. In Getgrav/grav, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Twig processing of static pages can be enabled in the front matter by any administrative user allowed to create or edit pages. As the Twig processor runs unsandboxed, this behavior can be used to gain arbitrary code execution and elevate privileges on the instance. ### Patches The issue was addressed by preventing dangerous functions from being called in Twig templates. A configuration option has been added to manually allow arbitrary PHP functions (`system.twig.safe_functions`) and filters (`system.twig.safe_filters`). Futures major versions of Grav may disable this functionality by default. ### Workarounds Blocking access to the `/admin` path from untrusted sources will reduce the probability of exploitation. ### References - https://portswigger.net/research/server-side-template-injection - https://blog.sonarsource.com/grav-cms-code-execution-vulnerabilities ### For more information If you have any questions or comments about this advisory, you can contact: - The original reporters, by sending an email to vulnerability.research [at] sonarsource.com; - The maintainers, by opening an issue on this repository.

CVE-2021-29440 Affected Getgrav/grav Versions

1 component(s)
Fixed Versions:
1.7.11
Product / Package Ecosystem Affected Versions Fixed Version
getgrav/grav
 Packagist
< 1.7.11
1.7.11

References

GitHub Advisory / Wiki ADVISORY
https://github.com/getgrav/grav/security/advisories/GHSA-g8r4-p96j-xfxc
NVD — CVE-2021-29440 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-29440
blog.sonarsource.com/grav-cms-code-execu... WEB
https://blog.sonarsource.com/grav-cms-code-execution-vulnerabilities
packagist.org/packages/getgrav/gr... WEB
https://packagist.org/packages/getgrav/grav
Getgrav/grav Security Information SECURITY
http://packetstormsecurity.com/files/162987/Grav-CMS-1.7.10-Server-Side-Template-Injection.html

Frequently Asked Questions

What is CVE-2021-29440?
CVE-2021-29440 is a security vulnerability in Getgrav/grav involving Grav's Twig processing allowing dangerous PHP functions by default under CWE-94: Improper Control of Generation of Code ('Code Injection').
Which Getgrav/grav versions are affected?
Affected versions include releases prior to 1.7.11 across affected packages: getgrav/grav.
What version fixes CVE-2021-29440?
Upgrading to 1.7.11 (or the latest patched release for your respective branch) resolves the vulnerability.
Is getgrav/grav affected?
Yes, getgrav/grav is affected in releases prior to 1.7.11. Upgrade your dependency to 1.7.11 or later.
What is the CVSS score of CVE-2021-29440?
CVE-2021-29440 has a CVSS v3.1 base score of 8.4 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H.
What CWE is associated with CVE-2021-29440?
CVE-2021-29440 is classified under CWE-94: Improper Control of Generation of Code ('Code Injection') (The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.).
How can I check Packagist dependencies for CVE-2021-29440?
Run the dependency tree command: 'inspect dependencies for getgrav/grav'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g8r4-p96j-xfxc",
  "modified" : "2022-08-11T00:01:25Z",
  "published" : "2021-04-16T19:53:12Z",
  "aliases" : [ "CVE-2021-29440" ],
  "summary" : "Grav's Twig processing allowing dangerous PHP functions by default",
  "details" : "### Impact\n\nTwig processing of static pages can be enabled in the front matter by any administrative user allowed to create or edit pages. \nAs the Twig processor runs unsandboxed, this behavior can be used to gain arbitrary code execution and elevate privileges on the instance.\n\n### Patches\n\nThe issue was addressed by preventing dangerous functions from being called in Twig templates. A configuration option has been added to manually allow arbitrary PHP functions (`system.twig.safe_functions`) and filters (`system.twig.safe_filters`). \n\nFutures major versions of Grav may disable this functionality by default. \n\n### Workarounds\n\nBlocking access to the `/admin` path from untrusted sources will reduce the probability of exploitation. \n\n### References\n\n- https://portswigger.net/research/server-side-template-injection\n- https://blog.sonarsource.com/grav-cms-code-execution-vulnerabilities\n\n### For more information\n\nIf you have any questions or comments about this advisory, you can contact:\n  - The original reporters, by sending an email to vulnerability.research [at] sonarsource.com;\n  - The maintainers, by opening an issue on this repository.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "getgrav/grav"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.7.11"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.7.10"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/security/advisories/GHSA-g8r4-p96j-xfxc"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-29440"
  }, {
    "type" : "WEB",
    "url" : "https://blog.sonarsource.com/grav-cms-code-execution-vulnerabilities"
  }, {
    "type" : "WEB",
    "url" : "https://packagist.org/packages/getgrav/grav"
  }, {
    "type" : "WEB",
    "url" : "http://packetstormsecurity.com/files/162987/Grav-CMS-1.7.10-Server-Side-Template-Injection.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-94" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-04-13T19:55:46Z",
    "nvd_published_at" : "2021-04-13T20:15:00Z"
  }
}