CVE-2026-46634: Twig Remote Code Execution Vulnerability

MODERATE
Advisory Identifier: GHSA-24x9-r6q4-q93w
Share
CWE-693
Published
Advisory Summary

CVE-2026-46634 is a MODERATE remote code execution vulnerability (CWE-693: Protection Mechanism Failure) affecting Twig libraries in the Packagist ecosystem. The issue involves `template_from_string()` escapes a sourcepolicy-driven sandbox via synthesized template name. Remediation is available by upgrading affected packages to version 3.26.0.

CVE-2026-46634 at a Glance

CVE Identifier CVE-2026-46634
GHSA Identifier GHSA-24x9-r6q4-q93w
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-693: Protection Mechanism Failure
Affected Product Twig
Package Ecosystem Packagist
Published Date
Last Updated

How to Fix CVE-2026-46634

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

twig/twig fixed: 3.26.0 
Upgrade twig/twig to 3.26.0
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 twig/twig

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-46634, inspect your project dependencies for Twig:

inspect dependencies for twig/twig

Analyze the terminal output to locate any version of Twig in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.26.0), 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-693: Protection Mechanism Failure, where the product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product. In Twig, 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

### Description When the sandbox is enabled selectively via `SourcePolicyInterface` (and not globally), a sandboxed template that is allowed to call `template_from_string` and `include` can render an arbitrary inner template with no security policy enforcement. `Environment::createTemplate()` compiles the inner string under a synthesized name (`__string_template__<hash>`), so a name/path-based `SourcePolicy` returns `false` for it, and the inner template's `checkSecurity()` becomes a no-op. From a template the integrator believes is sandboxed, an attacker can use any tag/filter/function (including `constant()` to read secrets, or `|map("system")` to execute shell commands). ### Resolution This is a configuration trap rather than a code bug: there is no legitimate use case for exposing `template_from_string` to untrusted template authors, and propagating the parent sandbox state through `template_from_string` would require invasive changes to `SourcePolicyInterface` semantics with their own risks. Starting with Twig 3.26.0, the documentation and the PHPDoc of `StringLoaderExtension::templateFromString()` explicitly warn against allowing `template_from_string` in a sandboxed environment (i.e. listing it in a `SecurityPolicy` allowed-functions list). Integrators using a `SourcePolicyInterface` MUST NOT allow `template_from_string` in their allowed functions; the safest option is not to register `StringLoaderExtension` at all when a sandbox is in use. ### Credits Twig would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue.

CVE-2026-46634 Affected Twig Versions

1 component(s)
Fixed Versions:
3.26.0
Product / Package Ecosystem Affected Versions Fixed Version
twig/twig
 Packagist
≥ 3.9.0
< 3.26.0
3.26.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/twigphp/Twig/security/advisories/GHSA-24x9-r6q4-q93w
Twig Source Repository REPOSITORY
https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/twig/CVE-2026-46634.yaml
Twig Source Repository REPOSITORY
https://github.com/twigphp/Twig
symfony.com/cve-2026-46634 WEB
https://symfony.com/cve-2026-46634

Frequently Asked Questions

What is CVE-2026-46634?
CVE-2026-46634 is a security vulnerability in Twig involving `template_from_string()` escapes a SourcePolicy-driven sandbox via synthesized template name under CWE-693: Protection Mechanism Failure.
Which Twig versions are affected?
Affected versions include releases prior to 3.26.0 across affected packages: twig/twig.
What version fixes CVE-2026-46634?
Upgrading to 3.26.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is twig/twig affected?
Yes, twig/twig is affected in releases prior to 3.26.0. Upgrade your dependency to 3.26.0 or later.
What CWE is associated with CVE-2026-46634?
CVE-2026-46634 is classified under CWE-693: Protection Mechanism Failure (The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.).
How can I check Packagist dependencies for CVE-2026-46634?
Run the dependency tree command: 'inspect dependencies for twig/twig'. 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-24x9-r6q4-q93w",
  "modified" : "2026-05-21T21:25:12Z",
  "published" : "2026-05-21T21:25:12Z",
  "aliases" : [ "CVE-2026-46634" ],
  "summary" : "Twig: `template_from_string()` escapes a SourcePolicy-driven sandbox via synthesized template name",
  "details" : "### Description\n\nWhen the sandbox is enabled selectively via `SourcePolicyInterface` (and not globally), a sandboxed template that is allowed to call `template_from_string` and `include` can render an arbitrary inner template with no security policy enforcement.\n\n`Environment::createTemplate()` compiles the inner string under a synthesized name (`__string_template__<hash>`), so a name/path-based `SourcePolicy` returns `false` for it, and the inner template's `checkSecurity()` becomes a no-op. From a template the integrator believes is sandboxed, an attacker can use any tag/filter/function (including `constant()` to read secrets, or `|map(\"system\")` to execute shell commands).\n\n### Resolution\n\nThis is a configuration trap rather than a code bug: there is no legitimate use case for exposing `template_from_string` to untrusted template authors, and propagating the parent sandbox state through `template_from_string` would require invasive changes to `SourcePolicyInterface` semantics with their own risks.\n\nStarting with Twig 3.26.0, the documentation and the PHPDoc of `StringLoaderExtension::templateFromString()` explicitly warn against allowing `template_from_string` in a sandboxed environment (i.e. listing it in a `SecurityPolicy` allowed-functions list). Integrators using a `SourcePolicyInterface` MUST NOT allow `template_from_string` in their allowed functions; the safest option is not to register `StringLoaderExtension` at all when a sandbox is in use.\n\n### Credits\n\nTwig would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue.",
  "severity" : [ ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "twig/twig"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.9.0"
      }, {
        "fixed" : "3.26.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/twigphp/Twig/security/advisories/GHSA-24x9-r6q4-q93w"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/twig/CVE-2026-46634.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/twigphp/Twig"
  }, {
    "type" : "WEB",
    "url" : "https://symfony.com/cve-2026-46634"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-693" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-21T21:25:12Z",
    "nvd_published_at" : null
  }
}