[GHSA] GHSA-g7gc-gmgp-wgqg (high) — eml_parser vulnerable to DoS via deeply nested parens in Received headers

GHSA-g7gc-gmgp-wgqg Severity: high CVE: CVE-2026-55620

eml_parser vulnerable to DoS via deeply nested parens in Received headers

### Summary

`eml_parser` strips parenthesised CFWS comments from `Received:` headers using a regex-based fix-point loop. The loop has quadratic time complexity in the number of nested parens. A single `Received:` header containing 5,000 nested parens causes ~1.3 secon