The pyasn1 library for Python prior to version 0.6.3 is 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 RecursionError or consumes all available memory. This vulnerability is distinct from CVE-2026-23490 which addressed integer overflows in OID decoding. Version 0.6.3 contains the fix for this specific recursion issue.