GHSA-529h-vh3j-85hq
Twig: Sandbox filter, tag and function allow-list bypass when sandbox state changes between renders for a cached `Template`
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
twig/twigReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Description
The per-template filter, tag and function allow-list check is compiled into the checkSecurity() method of each Template subclass and was invoked once from the constructor, gated by SandboxExtension::isSandboxed($source). Template instances are then cached on the Environment in $loadedTemplates, so the verdict computed at construction time was sticky for the rest of the process.
Any later change of sandbox state on the same Environment left that cached verdict in place: toggling SandboxExtension::enableSandbox()/disableSandbox(), swapping the policy via setSecurityPolicy(), a SourcePolicyInterface decision flip, or simply having a parent, macro or included template pre-instantiated outside the sandbox before a sandboxed render reached it. In all of these cases, the filters, tags and functions used by the affected template kept running with the original (typically empty) check, bypassing the SecurityPolicy allow-list.
Method, property and __toString allow-lists are not affected: they are enforced at every call site at runtime through SandboxExtension::checkMethodAllowed(), checkPropertyAllowed() and ensureToStringAllowed(), which re-read the current state on every call.
Long-lived workers (FrankenPHP, RoadRunner, Symfony Messenger consumers, FPM with hot autoloading) that share a single Environment between sandboxed and non-sandboxed renders are the most exposed: a single non-sandboxed render of a shared layout pre-warms its Template instance, after which any later sandboxed render that extends, uses, includes or imports from that layout silently skips the filter/tag/function allow-list for the pre-warmed instance.
Resolution
The allow-list check is no longer run from the constructor. Template gains a public ensureSecurityChecked() method that calls the compiled checkSecurity() only when SandboxExtension::isSandboxed($source) returns true for the current source, and it is invoked at every entry point that can reach a Template instance whose security has not yet been verified against the current state: Template::yield(), Template::yieldBlock() (on the resolved block template, which covers extends, use, traits and parent blocks), Template::getParent() (which evaluates user code when the parent name is dynamic) and Template::getTemplateForMacro() (on the resolved macro template).
The explicit checkSecurity() calls previously emitted by IncludeNode and CoreExtension::include() are removed: the included template's own yield() now re-runs the check against the current sandbox state. The compiled checkSecurity() body is a cheap walk over compile-time-static arrays, so the per-render cost is negligible. Old cached compiled PHP files keep working unchanged: the constructor-time call they still contain is idempotent.
Credits
Twig would like to thank Fabien Potencier for reporting and fixing the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | twig/twig | all versions | 3.27.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for twig/twig. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update twig/twig to 3.27.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-529h-vh3j-85hq is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-529h-vh3j-85hq is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-529h-vh3j-85hq. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-529h-vh3j-85hq in your dependencies?
O3 detects GHSA-529h-vh3j-85hq across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.