The pyasn1 library contains a denial of service vulnerability due to unbounded recursion when decoding ASN.1 data with deeply nested indefinite-length SEQUENCE or SET structures. An attacker can supply a crafted payload causing the decoder to recurse until the Python interpreter crashes with a RecursionError or exhausts memory, crashing the host application. This affects services parsing untrusted ASN.1 data such as LDAP, SNMP, Kerberos, or X.509 parsers. The vulnerability is fixed in pyasn1 version 5.20.0_1.