{
  "schema_version": "1.3.0",
  "slug": "beyond-what-complexity-and-linear-automaton-bounds-must-an-instance-constrain-regular-expression-matching-to-prevent-catastrophic-backtracking-denial-of-service",
  "title": "Beyond what complexity and linear-automaton bounds must an instance constrain regular-expression matching to prevent catastrophic backtracking denial-of-service?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** An AI instance, autonomous coding agent, or backend service authors regular expressions for input validation, routing, log parsing, tokenization, or user-driven text search. * **Does not apply when:** Using guaranteed li",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/beyond-what-complexity-and-linear-automaton-bounds-must-an-instance-constrain-regular-expression-matching-to-prevent-catastrophic-backtracking-denial-of-service.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/beyond-what-complexity-and-linear-automaton-bounds-must-an-instance-constrain-regular-expression-matching-to-prevent-catastrophic-backtracking-denial-of-service.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/beyond-what-complexity-and-linear-automaton-bounds-must-an-instance-constrain-regular-expression-matching-to-prevent-catastrophic-backtracking-denial-of-service.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 2571,
    "python_slice_tokens": 371,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "Autonomous systems frequently synthesize regular expressions (`re` in Python, `RegExp` in JavaScript, `java.util.regex`) to validate user inputs, parse log lines, or extract structured tokens from raw text. A foundational availability failure occurs when an instance treats **every regular expression as a fast $O(N)$ operation** while running on a backtrackin...",
    "what_was_observed": "In automated API validation, log-ingestion pipelines, and search-endpoint traces, instances operating without explicit regex-complexity and input-length bounds exhibit four primary failure modes: 1. **Nested Quantifier Exponential Hang (`(a+)+` / `([a-zA-Z0-9_]+\\.)+`):** An instance writes an email, domain, or slug validator using nested repetition such as `^([a-z0-9]+[-_]*)+\\$` or `^(\\w+\\s?)*\\$`. On valid inputs the...",
    "condition_of_validity": "* **Applies when:** An AI instance, autonomous coding agent, or backend service authors regular expressions for input validation, routing, log parsing, tokenization, or user-driven text search. * **Does not apply when:** Using guaranteed linear-time automaton engines (`google-re2`, Rust `regex` crate, Go `regexp` package) that compile patterns directly to DF...",
    "decision_boundary": "1. **Are you writing a regex with a quantifier (`+` or `*`) inside parentheses that also have a quantifier outside (`+` or `*`), like `([a-z]+_?)+`?** Stop immediately—that is a classic ReDoS time bomb. Rewrite it as `^[a-z]+(?:_[a-z]+)*\\$` so the separator is required between repetitions. 2. **Did you check `len(input_str) <= max_len` before calling `re.mat...",
    "operational_effect": "1. **Mandatory Pre-Regex Length Ceilings:** Across all generated validation and parsing routines, the instance checks `len(text) <= max_length` prior to invoking any regular expression engine. 2. **Unambiguous Separator-Anchored Quantifiers:** Whenever matching repeated tokens (slugs, domain labels, comma-separated lists), the instance emits flat `^token(?:s..."
  },
  "matched_failure_symptoms": [
    "REGEX_REDOS_CPU_LOCK"
  ],
  "composition_edges": {
    "primary_domain": "code_mutation_and_ast_patching",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/across-what-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes.md",
      "https://corpusfetch.com/c/across-what-encoding-and-canonicalization-boundaries-must-an-instance-normalize-identifiers-and-paths-to-prevent-equivalence-collision-and-bypass.md"
    ],
    "downstream_consequence_residuals": [
      "https://corpusfetch.com/c/across-what-concurrent-pipe-drain-and-ring-buffer-boundaries-must-an-instance-consume-subprocess-stdout-and-stderr-to-prevent-os-pipe-deadlocks-and-unbounded-output-oom.md",
      "https://corpusfetch.com/c/across-what-w3c-baggage-allowlist-and-pii-sanitization-gates-must-an-instance-propagate-cross-service-context-to-prevent-header-amplification-and-external-data-exfiltration.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/along-what-complexity-bounds-must-an-instance-arrest-premature-abstraction-and-speculative-over-engineering-when-synthesizing-solutions.md",
      "https://corpusfetch.com/c/along-what-decimal-and-integer-scaling-boundaries-must-an-instance-isolate-financial-and-precision-arithmetic-to-prevent-floating-point-drift-and-rounding-loss.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "b883576578c0a54c49543c9ff86c621649ba3a49c2a0bc976c1a41ad4dae499a",
    "verified_classes": [
      "LinearAutomatonRegexGuard"
    ],
    "verified_functions": [
      "verify_regex_pattern_safety",
      "bounded_regex_match",
      "validate_safe_slug",
      "safe_literal_or_prefix_filter"
    ],
    "verified_functions_count": 4,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "TypeError",
      "ValueError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "re",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}