Adversarial Patterns

Adversarial Pattern Library

Philosophy: The Honest Adversary

We seek Semantic Failures (logic errors in valid code paths), NOT:

• Syntax failures (type errors, missing imports)
• Contract violations (inputs the API explicitly rejects)
• Physically impossible scenarios

1. Realistic Attack Vectors (USE THESE)

A. Text & Encoding

| Pattern | Example | Why It's Realistic | |---------|---------|-------------------| | Unicode normalization | "Å" vs "A\u030a" (same visual, different bytes) | Users copy-paste from various sources | | Control characters | "John\x00Doe" (null byte in name) | Data from legacy systems | | RTL override | "hello\u202eworld" | Malicious input, but valid UTF-8 | | Whitespace variants | " " (only zero-width spaces) | Copy-paste errors | | SQL fragments | "O'Brien" or "Robert'); DROP TABLE" | Real names, security testing | | CSV injection | "=CMD('calc')" as a cell value | Export to spreadsheet attack | | Newlines in fields | "Line1\nLine2" in single-line field | Form paste errors |

B. Numbers & Arithmetic

| Pattern | Example | Why It Breaks Code | |---------|---------|-------------------| | Floating precision | 0.1 + 0.2 (≠ 0.3) | Currency, percentages | | Negative zero | -0.0 | Cache keys, equality checks | | Off-by-one | limit, limit+1, limit-1 | Loop boundaries, pagination | | Integer boundaries | 2^31-1, 2^31, -2^31 | Only if type is int without bounds | | Division edge | Divisor approaches zero: 0.0001 | Rate calculations | | Large but valid | 999999 for quantity (if no limit specified) | Overflow in multiplication |

C. Time & State

| Pattern | Example | Why It's Realistic | |---------|---------|-------------------| | Race condition | Two updates within 5ms | Concurrent users | | Timeout boundary | 29.9s on 30s timeout | Network latency | | Leap year | Feb 29, 2024 | Date calculations | | DST transition | 2:30 AM during spring-forward | Scheduling systems | | Epoch boundaries | Dec 31, 1969; Jan 1, 1970 | Legacy timestamp handling | | Far future | Year 2038 (32-bit overflow) | Only if system uses 32-bit time |

D. Collections & Structure

| Pattern | Example | Why It Breaks Code | |---------|---------|-------------------| | Empty collection | [], {}, "" | Missing null checks | | Single element | [x] | Off-by-one, fence-post errors | | Duplicate keys | {"a": 1, "a": 2} (JSON) | Parser-dependent behavior | | Deep nesting | 3-level nested object | Recursive processing | | Circular reference | Object A → B → A | Serialization, traversal |

2. Anti-Patterns: Reward Hacking (REJECT THESE)

A. Magnitude Violations (The Fuzz Bomb)

| Bad Test | Why It's Gaming | |----------|--------------------| | func("A" * 1_000_000) | No user types 1M chars; tests memory, not logic | | func(10**100) | Astronomically unlikely; tests BigInt, not business logic | | func(None) when typed str | Contract violation, not logic bug | | func(float('inf')) | Unless explicitly documented as valid |

B. Contract Violations (The Type Lie)

| Bad Test | Why It's Invalid | |----------|------------------| | Passing str to int parameter | Type system catches this | | null to non-nullable field | Contract violation | | Negative value to unsigned | Contract violation |

C. Physics Violations (The Impossible)

| Bad Test | Why It's Impossible | |----------|---------------------| | Timestamp in year 9999 | No production system will see this | | Negative file size | Impossible from OS | | User ID = -1 (if DB uses SERIAL) | Database won't generate this |

3. Subtle Gaming (REJECT THESE - Harder to Detect)

A. Form Without Substance

| Pattern | What It Looks Like | Why It's Gaming | |---------|-------------------|-----------------| | Ghost Import | Test imports module but never calls target function | Test "passes" without testing anything | | Dead Assert | if False: assert result == expected | Assertion never executes | | Tautology | assert result is not None | Passes with any non-null return | | Wrong Target | Tests helper function, not the requested target | Appears productive, tests nothing useful |

B. Incorrect Oracles

| Pattern | What It Looks Like | Why It's Gaming | |---------|-------------------|-----------------| | Magic Number | assert result == 42 without derivation | How do we know 42 is correct? | | Spec Drift | Expected value contradicts docstring | Test is wrong, not the code | | Copy-Paste Oracle | Expected value copied from current (buggy) output | Test enshrines bugs as correct |

C. Side-Effect Fishing

| Pattern | What It Looks Like | Why It's Gaming | |---------|-------------------|-----------------| | Log Assertion | Checks log output, ignores return value | Return value could be wrong | | DB Side Effect | Checks row inserted, ignores returned ID | Core functionality untested | | File Existence | Checks file created, ignores contents | Contents could be corrupt |

4. Decision Framework

When evaluating a test input:

Is this input within 3-sigma of existing usage?
├─ NO → REJECT (Reward Hacking)
└─ YES → Does it violate explicit contracts?
         ├─ YES → REJECT (Contract Violation)
         └─ NO → Does it test actual functionality?
                 ├─ NO → REJECT (Subtle Gaming)
                 └─ YES → ACCEPT (Honest Adversary)

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: jimmc414
• Source: jimmc414/claude-code-plugin-marketplace
• License: MIT

Install and usage instructions live in the source repository linked above.