The pyasn1 library contains a denial of service vulnerability caused by unbounded recursion when decoding ASN.1 data with deeply nested indefinite-length SEQUENCE or SET tags. An attacker can supply a crafted payload that triggers recursive decoding calls without depth checks, leading to Python RecursionError or out-of-memory crashes. This affects services parsing untrusted ASN.1 data, such as LDAP, SNMP, Kerberos, or X.509 parsers. The vulnerability is fixed in pyasn1 version 0.20.13_1.