HN · HACKER_NEWS// 21h agoSECURITY INCIDENT

Lean-zip bug exposes formal verification gaps

Lean-zip, a formally verified zlib implementation in Lean 4, was found to have a heap buffer overflow and DoS vulnerability. The failures stem from unverified components and a critical integer overflow bug in the Lean 4 runtime's memory allocation.

// ANALYSIS

The discovery of vulnerabilities in a "proven correct" program is a sobering reminder that formal verification is only as strong as its specification and the underlying runtime.

–A heap buffer overflow was found in the Lean 4 runtime (TCB), an area typically assumed to be correct by formal proofs
–An archive parser bug caused a DoS due to a specification gap where the parser logic wasn't covered by any theorems
–Fuzzing tools like AFL++ and AddressSanitizer remain essential, even for code with mathematical proofs of correctness
–The incident underscores that "correctness" in formal methods is relative to the model, not the absolute reality of execution

// TAGS

lean-zipleanformal-verificationtestingsafetyreasoningopen-source

DISCOVERED

21h ago

2026-04-14

PUBLISHED

1d ago

2026-04-14

RELEVANCE

8/ 10

AUTHOR

bumbledraven