Summary
A code injection weakness in ANTLR4's Grammar Action Block handling allows attacker-controlled grammar input to influence generated output files and injected code.
When untrusted or manipulated grammars are processed remotely, this flaw can enable execution of attacker-supplied code in environments that compile or run the generated artifacts.
A code injection weakness in ANTLR4's Grammar Action Block handling allows attacker-controlled grammar input to influence generated output files and injected code.
When untrusted or manipulated grammars are processed remotely, this flaw can enable execution of attacker-supplied code in environments that compile or run the generated artifacts.
Affected context
The issue arises in workflows that use ANTLR4 to process grammar files and generate code, particularly where grammar definitions or action blocks may be influenced by external or less trusted sources.
It is most relevant in build pipelines, tooling integrations, or hosted parsing services that automatically transform grammars into executable code without strong validation or isolation of embedded actions.
The issue arises in workflows that use ANTLR4 to process grammar files and generate code, particularly where grammar definitions or action blocks may be influenced by external or less trusted sources.
It is most relevant in build pipelines, tooling integrations, or hosted parsing services that automatically transform grammars into executable code without strong validation or isolation of embedded actions.
Exploit preconditions
- Attack surface: Grammar input to ANTLR4's code generation pipeline, including embedded action blocks.
- Required access: Ability to submit, modify, or influence the grammar files or templates consumed by ANTLR4 (e.g., via repository contribution, API upload, or configuration changes).
- Trigger point: Execution of ANTLR4's code generation on the crafted grammar and subsequent compilation or execution of the generated output files.
- Why exploitation is possible: Grammar action blocks are incorporated into generated code with insufficient sanitization or constraint, enabling attacker-controlled content to become executable logic.
- Attack surface: Grammar input to ANTLR4's code generation pipeline, including embedded action blocks.
- Required access: Ability to submit, modify, or influence the grammar files or templates consumed by ANTLR4 (e.g., via repository contribution, API upload, or configuration changes).
- Trigger point: Execution of ANTLR4's code generation on the crafted grammar and subsequent compilation or execution of the generated output files.
- Why exploitation is possible: Grammar action blocks are incorporated into generated code with insufficient sanitization or constraint, enabling attacker-controlled content to become executable logic.
Why this happens
The underlying bug class aligns with CWE-94: Improper Control of Generation of Code and CWE-74: Improper Neutralization of Special Elements in Output.
ANTLR4's Grammar Action Block Handler allows user-supplied action code to be embedded into generated output files, but does not adequately restrict or normalize the content before integrating it into compilable source.
This pattern treats grammar-embedded actions as inherently trusted, allowing arbitrary constructs, special characters, and language-specific code fragments to pass through, resulting in generated code that can execute attacker-specified logic when built or run.
The underlying bug class aligns with CWE-94: Improper Control of Generation of Code and CWE-74: Improper Neutralization of Special Elements in Output.
ANTLR4's Grammar Action Block Handler allows user-supplied action code to be embedded into generated output files, but does not adequately restrict or normalize the content before integrating it into compilable source.
This pattern treats grammar-embedded actions as inherently trusted, allowing arbitrary constructs, special characters, and language-specific code fragments to pass through, resulting in generated code that can execute attacker-specified logic when built or run.
Potential impact
- Attacker-controlled code may be compiled and executed as part of generated parsers or tooling.
- Build pipelines and continuous integration systems could run malicious logic during compilation or tests.
- Downstream applications using the generated parsers can inherit hidden execution paths or backdoors.
- Supply-chain risks may arise if compromised grammars are shared or reused across multiple projects.
- Attacker-controlled code may be compiled and executed as part of generated parsers or tooling.
- Build pipelines and continuous integration systems could run malicious logic during compilation or tests.
- Downstream applications using the generated parsers can inherit hidden execution paths or backdoors.
- Supply-chain risks may arise if compromised grammars are shared or reused across multiple projects.
General mitigation guidance
Mitigation generally focuses on reducing trust in grammar-provided actions and constraining how code is generated from user inputs.
Useful defensive patterns include:
- Treating grammar files and embedded actions as untrusted when they originate outside a tightly controlled development team.
- Restricting or disabling arbitrary action blocks in contexts where grammars are user-submitted or dynamically loaded.
- Introducing a strict validation layer that whitelists allowed constructs and rejects grammars containing unexpected or dangerous code patterns.
- Generating code within locked-down build environments and running the resulting artifacts with least-privilege execution profiles.
- Separating declarative grammar definitions from imperative action logic, keeping executable code in reviewed source files rather than in user-editable grammars.
Mitigation generally focuses on reducing trust in grammar-provided actions and constraining how code is generated from user inputs.
Useful defensive patterns include:
- Treating grammar files and embedded actions as untrusted when they originate outside a tightly controlled development team.
- Restricting or disabling arbitrary action blocks in contexts where grammars are user-submitted or dynamically loaded.
- Introducing a strict validation layer that whitelists allowed constructs and rejects grammars containing unexpected or dangerous code patterns.
- Generating code within locked-down build environments and running the resulting artifacts with least-privilege execution profiles.
- Separating declarative grammar definitions from imperative action logic, keeping executable code in reviewed source files rather than in user-editable grammars.
How teams detect issues like this
Detection efforts can focus on both the grammar inputs and the generated output code:
- Static analysis rules that flag direct inclusion of untrusted grammar action blocks into generated source files.
- Code review practices that require inspection of grammars and templates, especially those contributed by external parties or pulled from shared repositories.
- Build-time checks that search generated code for suspicious patterns, such as filesystem or network operations originating from grammar-embedded actions.
- Policy enforcement in CI/CD pipelines to block or quarantine grammars that do not meet predefined safety criteria.
- Use of automated code scanning tools to monitor generated artifacts and highlight unexpected or risky constructs introduced via code generation.
Detection efforts can focus on both the grammar inputs and the generated output code:
- Static analysis rules that flag direct inclusion of untrusted grammar action blocks into generated source files.
- Code review practices that require inspection of grammars and templates, especially those contributed by external parties or pulled from shared repositories.
- Build-time checks that search generated code for suspicious patterns, such as filesystem or network operations originating from grammar-embedded actions.
- Policy enforcement in CI/CD pipelines to block or quarantine grammars that do not meet predefined safety criteria.
- Use of automated code scanning tools to monitor generated artifacts and highlight unexpected or risky constructs introduced via code generation.
Sources
| Source | Link |
|---|---|
| github. | github.com/ |
| vuldb. | vuldb.com/ |
| vuldb. | vuldb.com/ |
| vuldb. | vuldb.com/ |
| vuldb. | vuldb.com/ |
