variant-analysis

Variant Analysis

When to Use

• A vulnerability was found and you need to check for similar patterns elsewhere
• A security advisory describes a bug class and you need to assess exposure
• Generalizing a specific bug fix into a broader detection rule
• Systematic sweep after a security incident to find related issues
• Building detection queries from a known vulnerability exemplar

When NOT to Use

• Initial discovery of novel vulnerability classes (use fuzzing or audit)
• Exact-match searching for a known CVE (just grep for the affected function)
• Runtime detection (use WAF or RASP)

Variant Analysis Workflow

1. Understand the Original Bug

• What is the root cause? (missing check, wrong type, logic error)
• What makes it exploitable? (untrusted input reaches vulnerable code)
• What is the minimal pattern that captures the essence?

2. Generalize the Pattern

• Abstract away specific variable names and values
• Identify the structural pattern (e.g., "unchecked cast after deserialization")
• Consider language-specific variations of the same concept

3. Search for Variants

# Grep for structural patterns
grep -rn "cast.*deserialize\|fromJson.*\.(int\|long)" --include="*.java" .

# Semgrep for semantic patterns
semgrep --config /path/to/variant-rule.yaml .

# CodeQL for deep data flow variants
codeql database analyze db variant-query.ql

4. Triage Results

• Confirm each match is actually reachable with untrusted input
• Assess exploitability (is there a viable attack path?)
• Prioritize by severity and exposure

5. Create Persistent Detection

• Write Semgrep/CodeQL rules to catch future instances
• Add to CI pipeline to prevent regressions
• Document the variant class for team awareness

Generalization Strategies

Original Bug	Generalized Pattern
SQL injection in getUserById	Any string concatenation in SQL query methods
XSS in renderComment	Any user input in HTML template without escaping
Path traversal in downloadFile	Any user input in filesystem path construction
Buffer overflow in parseHeader	Any unbounded copy from network input
Missing auth check in /api/admin	Any route handler without auth middleware

Tools for Variant Analysis

Tool	Strength	Best For
Semgrep	Fast pattern matching	Single-file structural variants
CodeQL	Deep data flow	Cross-function/file variants
grep/ripgrep	Quick text search	Simple string pattern variants
AST-grep	Structural code search	Language-aware structural matching

Anti-Patterns

Mistake	Problem
Only searching exact strings	Misses renamed or refactored variants
Ignoring different languages	Same bug class can exist in JS, Python, Go, etc.
Stopping at first match	Variant analysis requires exhaustive search
Not creating detection rules	Same variant will reappear in new code