Detecting eval / exec Usage

Overview

Dynamic-code-execution APIs (CWE-95 Eval Injection) let an application interpret a string as code at runtime. If the string contains anything user-controllable, the application has handed the attacker arbitrary code execution.

The defensive posture: don't use these APIs. The exceptions are narrow: rule engines, formula evaluators (spreadsheet = formulas), plugin systems with explicit sandboxing. For everything else, there's almost always a safer alternative.

When the skill produces findings

| Finding | Severity | Threshold | Affected control | |---|---|---|---| | Python eval(...) with non-literal | CRITICAL | argument contains var ref | CWE-95 | | Python exec(...) with non-literal | CRITICAL | argument contains var ref | CWE-95 | | Python compile(...) with non-literal | HIGH | source string contains var | CWE-95 | | Python __import__(var) | HIGH | dynamic module loading | CWE-95 | | JS eval(...) | CRITICAL | any | CWE-95 | | JS new Function(str) | CRITICAL | any non-literal | CWE-95 | | JS setTimeout/setInterval(string) | HIGH | string instead of function | CWE-95 | | Ruby eval(...)/instance_eval(...)/class_eval(...) | CRITICAL | non-literal | CWE-95 | | PHP eval(...) | CRITICAL | always | CWE-95 | | PHP assert($str) | CRITICAL | (legacy code-eval form) | CWE-95 | | PHP create_function | CRITICAL | deprecated, eval-equivalent | CWE-95 | | Java ScriptEngineManager + eval | HIGH | dynamic script execution | CWE-95 | | C# Activator.CreateInstance(Type.GetType(str)) | HIGH | type loading from string | CWE-95 |

Prerequisites

• Python 3.9+
• Source tree on local filesystem

Instructions

Run

bash
python3 ${CLAUDE_PLUGIN_ROOT}/skills/detecting-eval-exec-usage/scripts/scan_eval.py /path/to/repo

Options: --output FILE, --format json|jsonl|markdown, --min-severity, --include-tests, --languages LIST.

Interpret

CRITICAL = direct RCE vector. Replace the dynamic execution with explicit logic (lookup table, switch statement) or a sandboxed expression library (Python simpleeval, JavaScript expr-eval, Ruby Dentaku).

Remediation

See references/PLAYBOOK.md.

Examples

Pre-commit

bash
python3 ${CLAUDE_PLUGIN_ROOT}/skills/detecting-eval-exec-usage/scripts/scan_eval.py \
    --min-severity high $(git diff --name-only main...HEAD | tr '\n' ' ')

CI

yaml
- run: |
    python3 plugins/security/penetration-tester/skills/detecting-eval-exec-usage/scripts/scan_eval.py \
        . --min-severity high

Output

JSON / JSONL / Markdown. Exit codes: 0 / 1 / 2.

Error Handling

False positive on eval("'literal'") — the value is a constant string. Verify the regex match by reading the source line.

Resources

• references/THEORY.md — Why dynamic-code execution is the

highest-impact injection class, sandbox limits, the formula-evaluator design pattern

• references/PLAYBOOK.md — Per-language safe alternatives

(Python simpleeval / ast.literal_eval, JS expression-eval libraries, Ruby Dentaku, Java scripting sandboxes)