Twig Template Engine Flaw Allows Authenticated Code Execution
A validation bypass in Twig's PHP callable handling exposes applications to arbitrary code execution when source policies are enabled. Ubuntu has released a security patch addressing the vulnerability affecting authenticated users.
TL;DR
- Twig template engine contains a PHP callable validation flaw in source policy enforcement
- Authenticated attackers can exploit the bypass to execute arbitrary code on affected systems
- Ubuntu USN-8408-1 patch addresses the vulnerability across supported distributions
- Organizations using Twig with source policies should prioritize immediate patching
- The vulnerability highlights risks in template engine security configurations
Twig, a widely-used PHP template engine, contains a security flaw that undermines its source policy protections. The vulnerability stems from improper validation of PHP callables, allowing authenticated users to circumvent intended restrictions and execute arbitrary code on vulnerable systems.
This issue is particularly concerning for applications that rely on Twig's source policy as a security boundary between trusted and untrusted template contexts. The flaw demonstrates how template engine misconfigurations can create authentication-based code execution pathways that bypass application-level controls.
Ubuntu has released patch USN-8408-1 to address this vulnerability. Organizations running Twig-dependent applications should evaluate their exposure and apply updates promptly, especially in multi-tenant or user-generated-content scenarios.
Technical Details
- Vulnerability exists in Twig's PHP callable validation logic within source policy enforcement
- Authenticated users can craft malicious callables that bypass validation checks
- Source policies intended to restrict template execution are rendered ineffective
- Arbitrary code execution occurs in the context of the application's PHP process
Risk Assessment & Mitigation
- Requires prior authentication, limiting exposure to internal or registered users
- Organizations using Twig with source policies face elevated risk of privilege escalation
- Apply Ubuntu security patch USN-8408-1 across affected systems immediately
- Review template handling logic and source policy configurations post-patching
- Consider additional input validation layers for user-supplied template content
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