Executive brief
eml_parser is a library used by security operations centers (SOCs) to parse and analyze email messages. An attacker can craft a malicious email with unusually nested comment structures in the header fields (To, From, Cc, etc.) that causes the parser to crash with an unhandled error, preventing the email from being processed. While the impact is limited because organizations already need error handling for malformed emails, it could disrupt automated email analysis pipelines used for threat detection and incident response.
Technical details
The vulnerability exists in eml_parser's use of Python's standard library `email.utils.getaddresses()` function to parse email address headers. When processing headers with deeply nested CFWS (comment/folding white space) structures, the standard library's recursive descent parser exhausts the call stack and raises a RecursionError. Since eml_parser does not catch this exception, it propagates uncaught and aborts the entire email message parsing. No authentication or user interaction is required—an attacker simply sends a crafted EML file with pathological header nesting to any SOC pipeline using eml_parser. The fix, released in version 3.0.2, wraps the standard library parser call in error handling and falls back to a simpler regex-based parser when a RecursionError is detected.
Affected products
- GOVCERT-LU eml_parser < 3.0.2
Timeline
- 2026-06-15: disclosed: Vulnerability initially published in GitHub Advisory Database
- 2026: patched: Fix released in eml_parser version 3.0.2 with fallback regex-based parser
- 2026-08-25: advisory: Advisory updated and finalized