CVE-2026-59884: pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER codecs parses long-form tags by accumulating continuation octets without an

highCVSS 7.5CVE-2026-59884

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER codecs parses long-form tags by accumulating continuation octets without an upper bound on the tag ID size, allowing a crafted input to force construction of an arbitrarily large integer with CPU cost growing quadratically and to trigger unhandled ValueError exceptions in Python 3.11+ error formatting paths. Any application decoding untrusted BER, CER, or DER input is affected. This issue is fixed in version 0.6.4.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: high — CVSS 7.5
Published: 2026-07-14
Last updated: 2026-07-21
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-59884

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-598840.35% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 28% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-59884	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for pyasn1 is a

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

medium[UPDATE] [medium] Red Hat Enterprise Linux (pyasn1): Vulnerability allows Denial of Servicecert-bund · 2026-07-31
highGHSA-hm4w-wwcw-mr6r: pyasn1: Uncontrolled resource consumption when converting decoded REAL valuesghsa · 2026-07-21
highGHSA-8ppf-4f7h-5ppj: pyasn1: Quadratic complexity in OBJECT IDENTIFIER and RELATIVE-OID processing allows deni…ghsa · 2026-07-21
highGHSA-m4p7-r5rc-7g4j: pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDsghsa · 2026-07-21
highCVE-2026-59886: pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the univ.Real type converted its…nvd · 2026-07-14
highCVE-2026-59885: pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER, CER, and DER decoders p…nvd · 2026-07-14