CVE-2026-59884: pyasn1 is a generic ASN.1 library for Python

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HIGH 7.5REMOTEUPGRADE

CVE-2026-59884 is a high-severity flaw (CVSS 7.5) affecting pyasn1. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 B

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 51%)
CISA exploited list	No
Weakness	CWE-400
Published	2026-07-14
Last modified	2026-07-21

Publisher (CNA): GitHub, Inc. · Vendor: pyasn1

Last updated 2026-07-21 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-14 17:17 UTCPublished CVE record published
2026-07-21 14:37 UTCUpdated Record last modified

pyasn1 pyasn1 UPGRADE

Affected: < 0.6.4

Fixed in: 0.6.4

Safe to downgrade to: no unaffected older release

1. Check installed version

pip show pyasn1

2. UPGRADE to 0.6.4

pip install --upgrade "pyasn1>=0.6.4"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-59884?

pyasn1: upgrade to 0.6.4. Exact commands for each OS are on this page.

Is CVE-2026-59884 being exploited?

CVE-2026-59884 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-59884 affect?

CVE-2026-59884 affects pyasn1. Severity is high (CVSS 7.5). 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

How urgent is CVE-2026-59884?

Priority 44/100. High severity; Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities

Related CVEs

CVE-2026-59885 HIGH 7.5 UPGRADE pyasn1 is a generic ASN.1 library for Python
CVE-2026-59886 HIGH 7.5 UPGRADE pyasn1 is a generic ASN.1 library for Python

References

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