Twig Sandbox: Allow-List Bypass When Sandbox State Changes

Published as "Twig: Sandbox filter, tag and function allow-list bypass when sandbox state changes between renders for a cached `Template`"

high Symfony Twig · Last reviewed Nov 4, 2026

CVE: CVE-2026-49981
GHSA: GHSA-529h-vh3j-85hq
Packagist: PKSA-8zx5-v2nz-58pb
Reported: Jul 1, 2026

Lets an untrusted template use forbidden filters, tags and functions when one Twig environment renders both sandboxed and normal templates.

Affected and fixed versions

In twig/twig. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
Up to 3.26.0	No fix yet

What this means

An untrusted template rendered in Twig's sandbox can use filters, tags and functions your security policy doesn't allow. The sandbox checked a template's allowed filters, tags and functions once, when the template was first loaded, and kept that answer for the rest of the process.

Who is affected

Apps on twig/twig up to and including 3.26.0 that use the sandbox (SandboxExtension with a SecurityPolicy) and render both sandboxed and normal templates with the same Twig\Environment. The check could be skipped when:

enableSandbox() or disableSandbox() is called between renders
the policy is swapped with setSecurityPolicy()
a SourcePolicyInterface gives a different answer
a parent, macro or included template was first loaded outside the sandbox

The Twig advisory says long-running workers that share one environment are the most exposed: FrankenPHP, RoadRunner and Symfony Messenger consumers. Allowed methods, properties and __toString() are checked on every call, so those lists still held. Apps that don't use the sandbox aren't affected.

What to do

Update twig/twig to 3.27.0. Twig now runs the allow-list check every time a template is rendered, extended, included or imported from, using the current sandbox state. Older compiled template cache files keep working.

Reported and fixed by Fabien Potencier.

Check your app with an agent

Paste this into a coding agent that can read your project, such as Claude Code, Codex or Amp. It checks your composer.lock against the versions above and tells you what to update, without changing anything.

Check whether the PHP project you have access to is affected by this security advisory, and tell me what to update. Do a read-only check: don't edit files, don't run composer update or composer require, and don't try to reproduce the flaw.

Advisory: Twig Sandbox: Allow-List Bypass When Sandbox State Changes (CVE-2026-49981, GHSA-529h-vh3j-85hq)
Details: https://phpnews.net/security/symfony/ghsa-529h-vh3j-85hq

Affected versions, as Composer constraints:
- twig/twig: <=3.26.0

Fixed releases:
- Up to 3.26.0: no fixed release yet

1. Find every composer.lock in the project outside vendor/ (a monorepo can have one per app) and read the installed version of each package above. Packages installed as dependencies of other packages count too.
2. Compare each installed version with its constraint: "|" separates alternative ranges, and "," means both bounds apply.
3. For each affected install, read "What this means" at https://phpnews.net/security/symfony/ghsa-529h-vh3j-85hq and check whether the project meets the conditions it describes (a feature in use, a config value, a driver). Say which conditions you could check and which you couldn't.
4. Report a table: lock file | package | installed version | affected (yes, no or unknown) | conditions met (yes, no or unknown) | update to | evidence. For each affected package, give the command that would fix it, without running it: composer update <package> --with-dependencies when it is only installed as a dependency of another package, or composer require with the fixed version when composer.json requires it directly. If the installed version is on a branch with no fixed release listed, say it needs a move to a newer branch.

Sources

← All Twig advisories