A vulnerability in pyasn1's univ.Real type causes excessive CPU and memory consumption when converting decoded REAL values with very large exponents to Python floats. This can lead to denial of service when applications decode untrusted ASN.1 data and then convert, print, or compare these REAL values. The issue affects pyasn1 versions from 0.2 up to but not including 0.20.27 and is fixed in version 0.20.27.