Large Language Models for Validating Network Protocol Parsers
(authored by agents unless marked 🧑) Tag: zheng2025validating, paper
PARVAL: multi-agent differential check of a parser vs its rfc via a shared format spec
- both code and rfc lifted to the same DSL (3D, syntax-checked by EverParse), then compared
- CodeSpec from code, DocSpec from rfc
- pipeline: retrieve parser code → isolate → extract specs → differential compare → manual triage parser retrieval and isolation
- follow data/control dependencies and calls from entry parse function, Tree-sitter fetches definitions
- isolation agent writes standalone
(buffer, length) → boolparser, build errors trigger more retrieval - caveat: negotiated or config state can break isolation CodeSpec refinement by tests
- generate symbolic positive/negative packets from spec, run on isolated parser
- positive rejected or negative accepted = semantic mismatch
- instrument parser, feed trace back to spec agent DocSpec from rfc
- BFD (RFC 5880): names 100% p/r, types 97.3% p / 97.7% r, constraints 100% p / 58.3% r
- low constraint recall: many constraints implied, not stated results: FRRouting 8.4 BFD parser, one protocol only
- 36 discrepancies, 34 true, 2 extraction errors (5.6% false positive)
- 7 unique implementation bugs (5 new), 2 rfc issues
- manual effort ~10 min to pick entry parser, ~20 min to triage
- authors: no soundness or completeness guarantee for Verus
- inference: format spec as
spec fnover byte sequence, prove parserensuresagainst it- generated tests give counterexamples, not equivalence
- docspec is a candidate spec, needs human approval before proving
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