Add fuzz testing for GitHub expression parser security validation

[Copilot]

Fuzz Testing for GitHub Expression Parser ✅

This PR implements comprehensive fuzz testing for the GitHub expression parser to validate security controls against malicious expression injection attempts, completing issue #3836.

📦 Implementation Summary

Files Created:

• pkg/workflow/expression_parser_fuzz_test.go - Comprehensive fuzz test with 59 seed cases

Files Modified:

• TESTING.md - Added fuzz test section with documentation and usage examples
• .github/workflows/super-linter.lock.yml - Updated to SHA-pinned action references
• .github/workflows/ci.yml - Added fuzz test job to CI pipeline (runs for 10s)

🧪 Test Coverage

The fuzz test includes 59 carefully crafted seed cases covering:

1. Allowed GitHub Expressions (12 seeds) - Basic context, event data, job outputs
2. Complex Expressions (4 seeds) - Logical operators (&&, ||, !), nested expressions
3. Malicious Injection Attempts (4 seeds) - Secret access, mixed valid/invalid patterns
4. Script Tag Injection (3 seeds) - XSS attempts, data exfiltration
5. Command Injection (3 seeds) - Shell commands, backticks, dollar paren
6. Edge Cases - Malformed (8 seeds) - Empty, whitespace, missing delimiters
7. Edge Cases - Nested (5 seeds) - Double/triple nesting, unicode
8. Edge Cases - Long (2 seeds) - Very long expressions with 100+ terms
9. Additional Attack Patterns (18 seeds) - SQL injection, URL encoding, null bytes

✅ Test Results

Baseline Test (Seed Corpus Only):

go test -run FuzzExpressionParser ./pkg/workflow/

• ✅ All 59 seeds executed successfully
• ✅ No panics or crashes

Fuzz Test (10 seconds):

go test -fuzz=FuzzExpressionParser -fuzztime=10s ./pkg/workflow/

• ✅ Generated ~66,000 test cases
• ✅ Rate: ~4,300-8,500 exec/sec
• ✅ Found 22 new interesting cases
• ✅ No crashes or panics
• ✅ Total runtime: ~58 seconds (including compilation and setup)

🔒 Security Validation

The fuzz test successfully validates that the expression parser:

✅ Accepts all allowed GitHub context expressions

• Core GitHub context (github.workflow, github.repository, etc.)
• Complex logical expressions with operators
• Nested expressions with proper parentheses

✅ Rejects unauthorized expressions

• Secret access patterns (secrets.GITHUB_TOKEN)
• Unauthorized context access (github.token)
• Provides clear error messages

✅ Blocks injection attack attempts

• Script tag injection
• Command injection patterns
• SQL injection patterns

✅ Handles edge cases without panic

• Empty and malformed expressions
• Very long expressions (100+ terms)
• Nested delimiters and special characters
• Unicode and control characters

📚 Documentation

Updated TESTING.md with:

• New "Fuzz Tests" section between Unit Tests and Benchmarks
• Usage examples for different fuzzing scenarios
• CI/CD integration guidance
• Expected results and corpus location

🔄 CI Integration

Added fuzz job to .github/workflows/ci.yml:

• Runs FuzzExpressionParser for 10 seconds on every push and PR
• Total job runtime: under 1 minute including setup
• Uses same Go setup and caching as other test jobs
• Runs in parallel with other CI jobs using concurrency groups

🎯 Acceptance Criteria

All acceptance criteria from issue #3836 have been met:

• Fuzz test function created with appropriate seed corpus
• Seeds include both allowed and disallowed expression patterns
• Unauthorized expressions are consistently rejected
• Parser handles all fuzzer-generated inputs without panic
• Test runs successfully with go test -fuzz=FuzzExpressionParser -fuzztime=10s
• No bypasses or edge cases discovered during fuzzing
• Documentation updated in TESTING.md
• CI integration added to run fuzz tests automatically

🚀 Usage

Run the fuzz test:

# Quick test (10 seconds) - used in CI
go test -fuzz=FuzzExpressionParser -fuzztime=10s ./pkg/workflow/

# Extended test (1 minute)
go test -fuzz=FuzzExpressionParser -fuzztime=1m ./pkg/workflow/

# Run seed corpus only (no fuzzing)
go test -run FuzzExpressionParser ./pkg/workflow/

💡 Recommendations

1. ✅ Fuzz test added to CI pipeline with 10s time limit (under 1 minute total)
2. Monitor corpus for new interesting cases
3. Run extended fuzzing (1h+) periodically for deeper testing
4. Investigate any new crashes or edge cases discovered

🔗 Related

Part of testing improvement initiative from discussion #3811

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[task] Add fuzz tests for GitHub expression parser</issue_title>
<issue_description>## Objective
Implement fuzz testing for the GitHub expression parser to validate security controls against malicious expression injection attempts.

Context

This is part of the testing quality improvement initiative (discussion #3811). The expression parser validates GitHub Actions expressions in workflow files, which is security-critical for preventing injection attacks. Fuzz testing helps ensure the allowlist-based validation is robust.

Approach

1. Create pkg/workflow/expression_parser_fuzz_test.go
2. Implement func FuzzExpressionParser(f *testing.F)
3. Seed the fuzzer with:
   • Allowed GitHub expressions from the security allowlist
   • Potentially malicious injection attempts (script tags, command injection patterns)
   • Edge cases (empty expressions, very long expressions, nested delimiters)
4. Verify unauthorized expressions are properly rejected
5. Ensure no panic on malformed input

Files to Modify

• Create: pkg/workflow/expression_parser_fuzz_test.go
• Reference: pkg/workflow/expression_safety.go (validation logic)
• Reference: pkg/workflow/expression_safety_test.go (for seed data)

Acceptance Criteria

• Fuzz test function created with appropriate seed corpus
• Seeds include both allowed and disallowed expression patterns
• Unauthorized expressions are consistently rejected
• Parser handles all fuzzer-generated inputs without panic
• Test runs successfully with go test -fuzz=FuzzExpressionParser -fuzztime=10s
• Any discovered bypasses or edge cases are documented

Related

Part of testing improvement task 1 from discussion #3811
Related to #3811

AI generated by Plan Command for discussion #3811</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [task] Add fuzz tests for GitHub expression parser #3815

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[Copilot]

Pull Request Overview

This PR implements comprehensive fuzz testing for the GitHub expression parser to validate security controls against malicious expression injection attempts. The implementation includes 59 seed test cases and integrates with Go's built-in fuzzing framework to discover edge cases and ensure the parser handles all inputs without panicking.

Key changes:

• Created expression_parser_fuzz_test.go with comprehensive seed corpus covering allowed expressions, malicious injections, and edge cases
• Updated TESTING.md with fuzz test documentation including usage examples and CI/CD guidance
• Updated GitHub Actions dependencies to newer versions (super-linter to v8.2.1, upload/download artifacts to newer SHAs)

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
pkg/workflow/expression_parser_fuzz_test.go	New fuzz test with 59 seed cases validating expression parser security controls, including allowed GitHub expressions, malicious injection attempts (secrets, script tags, command injection), and edge cases (empty, malformed, nested delimiters)
TESTING.md	Added comprehensive fuzz testing documentation section with usage examples, available tests, expected results, and CI/CD integration guidance
.github/workflows/super-linter.lock.yml	Updated action versions: super-linter to v8.2.1, download-artifact and upload-artifact to newer SHA commits

---

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[Copilot]

The containsUnauthorizedPattern helper function uses a manual substring search implementation instead of the standard library's strings.Contains function. This is unnecessarily complex and less performant.

Consider using:

func containsUnauthorizedPattern(content string) bool {
    unauthorizedPatterns := []string{
        "secrets.GITHUB_TOKEN",
        "secrets.API_KEY",
        "secrets.TOKEN",
        "secrets.MY_SECRET",
        "github.token",
    }
    
    for _, pattern := range unauthorizedPatterns {
        if strings.Contains(content, pattern) {
            return true
        }
    }
    
    return false
}

[Copilot]

Updated to use strings.Contains instead of manual substring search in commit 13cfd0c. This simplifies the code and improves performance.

[Copilot]

This action reference uses a tag (v8.2.1) instead of a commit SHA. According to the security best practices in the developer instructions (Security Best Practices > Supply Chain Security > Pin Action Versions with SHA), all action versions should be pinned to SHA commits with version comments for security.

Use SHA-pinned version instead:

uses: super-linter/super-linter@<sha> # v8.2.1

This prevents tag hijacking attacks where tags can be deleted and recreated to point to malicious code.

Suggested change

	uses: super-linter/super-linter@v8.2.1
	uses: super-linter/super-linter@b7e7e6e2c3e8e8e79e2c1e1e7e2e1e7e2e1e7e2e # v8.2.1

[Copilot]

Added version comment to SHA-pinned action reference in commit 13cfd0c. The action now uses super-linter/super-linter@2bdd90ed3262e023ac84bf8fe35dc480721fc1f2 # v8.2.1 following security best practices.

[pelikhan]

@copilot apply comments

[pelikhan]

@copilot

• merge main, lint
• add fuzz job in ci.yml to run fuzz tests

[Copilot]

@copilot

• merge main, lint
• add fuzz job in ci.yml to run fuzz tests

Completed in commit 9bd3d66:

• Merged main branch (resolved merge conflict in super-linter.lock.yml)
• Ran make fmt and make lint - all checks passed
• Added fuzz job to .github/workflows/ci.yml that runs FuzzExpressionParser for 30s on every push and PR

[pelikhan]

@copilot make fuzz run for less than a minute. Here is a log https://github.com/githubnext/gh-aw/actions/runs/19328922433/job/55287342344#step:5:1

[Copilot]

@copilot make fuzz run for less than a minute. Here is a log https://github.com/githubnext/gh-aw/actions/runs/19328922433/job/55287342344#step:5:1

Reduced fuzz time from 30s to 10s in commit 6adc297. The entire fuzz job now completes in under 1 minute (~58 seconds total including compilation and setup).