6

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-49981

CVE-2026-49981: Twig: Sandbox filter, tag and function allow-list bypass when sandbox state changes between renders for a cached `Template`

Twig is a template language for PHP. Prior to 3.27.0, the per-template filter, tag, and function allow-list verdict is computed when a Template instance is constructed and can remain cached after sandbox state changes between renders, allowing a later sandboxed render to reuse a template that was originally checked with a different or empty policy. This issue is fixed in version 3.27.0.

(GitHub Advisory)

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CVE-2026-49981

CVE-2026-49981:

6

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
twig/twig	composer	<= 3.26.0	3.27.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability in Twig (GHSA-529h-vh3j-85hq) was a sandbox bypass caused by improper caching of security checks. The checkSecurity() method was only called once when a template was first loaded and cached. If the sandbox settings were changed later (e.g., by enabling the sandbox for a subsequent request), the cached template would continue to use the old, less restrictive security policy, leading to a sandbox escape.

The fix was to introduce a new method, ensureSecurityChecked(), which is now called from several key template rendering functions. This ensures that the security policy is re-evaluated for every render, even for cached templates.

The identified vulnerable functions are the ones that were modified to call ensureSecurityChecked(). Before the patch, these functions were the entry points for exploiting the vulnerability, as they would render templates using the cached, and potentially outdated, security information. An attacker could exploit this by first having the application render a template in a non-sandboxed context, and then trigger a render of the same template in a sandboxed context, bypassing the sandbox restrictions.

Vulnerable functions

Twig\Template::yield

src/Template.php

This is the main method for rendering a template. The patch adds a call to `ensureSecurityChecked()` at the beginning of the `yield` method. Before this change, the method would render a cached template without re-evaluating the sandbox security policy. This allowed an attacker to bypass the sandbox if the sandbox state was changed after the template was cached.

Twig\Template::yieldBlock

src/Template.php

This method renders a specific block of a template. Similar to `yield()`, it was vulnerable because it did not re-check the security policy for cached templates. The patch adds a call to `ensureSecurityChecked()` to fix this vulnerability.

Twig\Template::getParent

src/Template.php

This method is used to get the parent of a template. When the parent name is dynamic, it can evaluate user expressions. Before the patch, this could happen without a proper security check, allowing a sandbox bypass. The patch adds a call to `ensureSecurityChecked()` to prevent this.

Twig\Template::getTemplateForMacro

src/Template.php

This method is used to find the template that contains a specific macro. It could be used to access a pre-warmed (cached) template that was not correctly sandboxed. The patch adds calls to `ensureSecurityChecked()` to ensure the security policy is enforced.

Twig\Extension\CoreExtension::include

src/Extension/CoreExtension.php

This function is used to include another template. The patch removes an explicit, but insufficient, security check. The check is now handled by `Template::yield()`. The existence of this removed code indicates that this function was part of the vulnerable execution path, as it could be used to render a template with a stale security policy.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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