The pyasn1 Python library versions prior to 0.6.3 are vulnerable to a Denial of Service attack through uncontrolled recursion when decoding ASN.1 data with deeply nested structures. Attackers can craft payloads with thousands of nested SEQUENCE or SET tags with Indefinite Length markers, causing the decoder to recursively call itself until the Python interpreter crashes with a RecursionError or runs out of memory. This vulnerability is distinct from CVE-2026-23490 and affects the core ASN.1 decoding functionality. Version 0.6.3 addresses this specific recursion issue.