CVE-2026-59886: pyasn1: Uncontrolled resource consumption when converting decoded REAL values

The univ.Real type converted its (mantissa, base, exponent) value to a Python float using exact big-integer exponentiation. A BER/CER/DER-encoded REAL value only a few bytes long can carry a very large exponent, causing this computation to attempt to materialize an astronomically large integer.

Any operation that triggers float conversion on such a decoded value — prettyPrint(), str(), comparison, arithmetic, or an explicit float() call — consumes excessive CPU and memory, hanging the process. Applications that decode untrusted ASN.1 data and then print, log, or compare the decoded objects are vulnerable to denial of service. Decoding alone does not trigger the issue.