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HighVulnerabilityCVE-2026-119195updated 30 Oct 2026, 23:04 UTC

pyasn1 can be slowed to a crawl by specially crafted ASN.1 data

Someone can send a specially built block of data that makes a program using pyasn1 spend a lot of processing time on it. Enough of these can tie up the server's CPU and slow or stop the service.

Fixed in pyasn1 0.6.5 · out Official, 2 sources
SeverityHighCVSS 7.5 of 10
Being exploited?UnclearNo reports either way yet
Fix available?Yespyasn1 0.6.5 · since 30 Oct 2026
How sure is this?Official, 2 sourcesBacked by an official source

How the attack works simplified

  1. 1Attacker sends dataCrafted ASN.1 with many fragments
  2. 2Request reaches appApp decodes the untrusted input
  3. 3pyasn1 decodesRepeatedly copies the growing value
  4. 4CPU saturatesWorkers stall under quadratic work
  5. ResultService slows down or stops responding

What happened

In pyasn1 0.6.4 and earlier, decoding constructed OCTET STRING, character string, or indefinite-length ANY values with many fragments repeatedly copies the growing value, causing quadratic CPU work in BER, CER, and some DER paths.

Why it is dangerous: Applications that decode untrusted ASN.1 input can suffer CPU exhaustion and denial of service; there is no confidentiality or integrity impact.

Are you affected?

You are affected if you use pyasn1 0.6.4 or earlier to decode attacker-controlled BER, CER, or DER data, including constructed strings or indefinite-length ANY values.

Package / productAffected versionsFixed in
pyasn1 · pip<= 0.6.40.6.5

What to do

  1. Upgrade pyasn1 to 0.6.5 or later (pip install --upgrade pyasn1).
  2. If you cannot upgrade yet, limit or reject untrusted ASN.1 input before decoding.
  3. Check your dependencies with pip show pyasn1 to find where it is used.

Timeline

  1. 29 Oct 2026, 20:17 UTC
    Publicly disclosed
  2. 29 Oct 2026, 20:17 UTC
    Reported by NVD · NVD
  3. 29 Oct 2026, 20:21 UTC
    Picked up by Zero Radar
  4. 30 Oct 2026, 23:04 UTC
    GitHub Advisory reported on it · GitHub Advisory
  5. 30 Oct 2026, 23:04 UTC
    Fixed version published: pyasn1 0.6.5 · GitHub Advisory

Sources 2 reports, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
CVE-2026-119195 · GHSA-9m75-vc3g-4x39
CVSS
7.5 / 10
Disclosed
29 Oct 2026, 20:17 UTC
On Zero Radar
29 Oct 2026, 20:21 UTC (4 min after disclosure)
Last change
30 Oct 2026, 23:04 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

pyasn1 can be slowed to a crawl by specially crafted ASN.1 data · Zero Radar