CVE-2026-48806: Twig Sandbox `__toString()` Policy Bypass Vulnerability

MODERATE
Advisory Identifier: GHSA-5v5v-ww74-355v
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CWE-693 CWE-863
Published
Advisory Summary

CVE-2026-48806 is a MODERATE sandbox `__tostring()` policy bypass vulnerability (CWE-693: Protection Mechanism Failure) affecting Twig libraries in the Packagist ecosystem. The issue involves sandbox `__tostring()` policy bypass via dynamic mapping keys. Remediation is available by upgrading affected packages to version 3.27.0.

CVE-2026-48806 at a Glance

CVE Identifier CVE-2026-48806
GHSA Identifier GHSA-5v5v-ww74-355v
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-2026-48806

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: 3.27.0 
Upgrade twig/twig to 3.27.0
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-2026-48806, 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 3.27.0), 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 This is a residual bypass of CVE-2026-47732 / GHSA-pr2w-4gpj-cpq4 left after the initial fix for unguarded `__toString()` calls. In 3.26.0 the sandbox visitor was extended to wrap every child node that its parent will string-coerce at runtime with `CheckToStringNode`, gated by the new `CoercesChildrenToStringInterface`. `ArrayExpression` did not implement the interface for its mapping keys: when a dynamic key expression resolves to a `Stringable` object, `ArrayExpression::compile()` emits a raw `(string)` cast (via `StringCastUnary` for `ContextVariable` keys, and no cast at all for richer key expressions). PHP then invokes `__toString()` directly, without ever calling `SandboxExtension::ensureToStringAllowed()`. A sandboxed template author can therefore trigger `__toString()` on any object reachable in the render context by using it as a dynamic mapping key, for example: ```twig {% set arr = {(obj): "value"} %} ``` Direct output of the same object is correctly blocked, which makes this a clear policy enforcement gap. The reliable demonstrated impact is unauthorised disclosure of data returned by `__toString()`. ### Resolution `ArrayExpression` now declares its dynamic mapping keys as string-coercion sites through `CoercesChildrenToStringInterface`, so the sandbox visitor wraps them with `CheckToStringNode` and the policy is consulted before PHP coerces the key to a string. The compiler also keeps an explicit `(string)` cast around the wrapped expression so PHP type errors on non-string keys are preserved. As a side effect, any expression is now accepted as a dynamic mapping key (not only context variables); this is documented as a new feature on the 3.x branch. ### Credits Twig would like to thank El Kharoubi Iosif for reporting the issue and Fabien Potencier for providing the fix.

CVE-2026-48806 Affected Twig Versions

1 component(s)
Fixed Versions:
3.27.0
Product / Package Ecosystem Affected Versions Fixed Version
twig/twig
 Packagist
< 3.27.0
3.27.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/twigphp/Twig/security/advisories/GHSA-5v5v-ww74-355v
Twig Source Repository REPOSITORY
https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/twig/CVE-2026-48806.yaml
Twig Source Repository REPOSITORY
https://github.com/twigphp/Twig
Twig Release RELEASE
https://github.com/twigphp/Twig/releases/tag/v3.27.0
symfony.com/blog/cve-2026-48806... WEB
https://symfony.com/blog/cve-2026-48806-sandbox-tostring-policy-bypass-via-dynamic-mapping-keys

Frequently Asked Questions

What is CVE-2026-48806?
CVE-2026-48806 is a security vulnerability in Twig involving Sandbox `__toString()` policy bypass via dynamic mapping keys under CWE-693: Protection Mechanism Failure.
Which Twig versions are affected?
Affected versions include releases prior to 3.27.0 across affected packages: twig/twig.
What version fixes CVE-2026-48806?
Upgrading to 3.27.0 (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 3.27.0. Upgrade your dependency to 3.27.0 or later.
What CWE is associated with CVE-2026-48806?
CVE-2026-48806 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-2026-48806?
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-5v5v-ww74-355v",
  "modified" : "2026-06-30T18:42:49Z",
  "published" : "2026-06-30T18:42:49Z",
  "aliases" : [ "CVE-2026-48806" ],
  "summary" : "Twig: Sandbox `__toString()` policy bypass via dynamic mapping keys",
  "details" : "### Description\n\nThis is a residual bypass of CVE-2026-47732 / GHSA-pr2w-4gpj-cpq4 left after the initial fix for unguarded `__toString()` calls.\n\nIn 3.26.0 the sandbox visitor was extended to wrap every child node that its parent will string-coerce at runtime with `CheckToStringNode`, gated by the new `CoercesChildrenToStringInterface`. `ArrayExpression` did not implement the interface for its mapping keys: when a dynamic key expression resolves to a `Stringable` object, `ArrayExpression::compile()` emits a raw `(string)` cast (via `StringCastUnary` for `ContextVariable` keys, and no cast at all for richer key expressions). PHP then invokes `__toString()` directly, without ever calling `SandboxExtension::ensureToStringAllowed()`.\n\nA sandboxed template author can therefore trigger `__toString()` on any object reachable in the render context by using it as a dynamic mapping key, for example:\n\n```twig\n{% set arr = {(obj): \"value\"} %}\n```\n\nDirect output of the same object is correctly blocked, which makes this a clear policy enforcement gap. The reliable demonstrated impact is unauthorised disclosure of data returned by `__toString()`.\n\n### Resolution\n\n`ArrayExpression` now declares its dynamic mapping keys as string-coercion sites through `CoercesChildrenToStringInterface`, so the sandbox visitor wraps them with `CheckToStringNode` and the policy is consulted before PHP coerces the key to a string. The compiler also keeps an explicit `(string)` cast around the wrapped expression so PHP type errors on non-string keys are preserved.\n\nAs a side effect, any expression is now accepted as a dynamic mapping key (not only context variables); this is documented as a new feature on the 3.x branch.\n\n### Credits\n\nTwig would like to thank El Kharoubi Iosif for reporting the issue and Fabien Potencier for providing the fix.",
  "severity" : [ ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "twig/twig"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.27.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.26.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/twigphp/Twig/security/advisories/GHSA-5v5v-ww74-355v"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/twig/CVE-2026-48806.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/twigphp/Twig"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/twigphp/Twig/releases/tag/v3.27.0"
  }, {
    "type" : "WEB",
    "url" : "https://symfony.com/blog/cve-2026-48806-sandbox-tostring-policy-bypass-via-dynamic-mapping-keys"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-693", "CWE-863" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-30T18:42:49Z",
    "nvd_published_at" : null
  }
}