CVE-2026-59886 is a denial-of-service vulnerability in the pyasn1 library's handling of ASN.1 REAL values. The issue arises when converting decoded REAL values with very large exponents to Python floats, causing excessive CPU and memory consumption that can hang the process. This affects pyasn1 versions from 8.11.0 up to but not including 10.2.1. The vulnerability is triggered by operations such as printing, logging, or comparing decoded REAL objects from untrusted ASN.1 data. It does not occur during decoding alone. The issue is fixed in pyasn1 version 10.2.1.