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 tags. An attacker can supply crafted payloads that cause the decoder to recurse until the Python interpreter crashes with a RecursionError or exhausts system memory, leading to service crashes or resource exhaustion. This affects services using pyasn1 for ASN.1 parsing, such as LDAP, SNMP, Kerberos, and X.509 parsers. The vulnerability is fixed in version 0.2.2_12.