CVE-2026-119197: pyasn1: Quadratic-complexity denial of service in binary REAL decoding

Vulnerability summary

CVE-2026-119197 is a high (CVSS 7.5) Inefficient Algorithmic Complexity vulnerability in pyasn1. EPSS estimates a 0.43% chance of exploitation in the next 30 days, higher than 36.8% of scored vulnerabilities.

Timeline

1. 29-10-2026
   PublishedVulnerability first disclosed.
2. 30-10-2026
   Last modifiedVulnerability information updated.

Description

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.5, binary REAL decoding builds a large mantissa one octet at a time by shifting a growing integer and slicing the remaining byte string. Attacker-controlled ASN.1 includes a binary-encoded REAL with a large mantissa and reaches BER, CER, or DER decode(), with or without a schema containing REAL. RealPayloadDecoder.valueDecoder repeatedly performs a left shift, OR, and suffix copy for every mantissa octet, making decode time quadratic in mantissa length. A comparatively small REAL value can hold a decoding worker on one CPU core for seconds or longer and cause availability loss. This issue is fixed in version 0.6.5.

• CWE-407Inefficient Algorithmic ComplexityAn algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.