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HighVulnerabilityCVE-2026-119194updated 30 Oct 2026, 23:04 UTC

pyasn1 decoder can be slowed to a crawl by crafted input

A specially crafted small piece of data can make programs that read certain security-related data formats use a lot of processor time. This can slow down or stall the service reading it.

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 crafted dataSmall valid input with many colliding long tag IDs
  2. 2Data reaches the serviceApplication passes bytes to schemaless decoder
  3. 3Decoder slows downEach insertion compares against earlier colliding tags
  4. 4CPU is exhaustedRepeated inputs consume processor time
  5. ResultService becomes slow or unavailable

What happened

In pyasn1 versions 0.3.3 up to 0.6.5, schemaless BER, CER, and DER decoding inserts every component's TagSet into a growing set; attacker-chosen long tag IDs with colliding hashes make each insertion compare against all earlier colliding tags, causing quadratic CPU work.

Why it is dangerous: Repeated crafted inputs can exhaust decoder CPU and reduce service availability. No confidentiality or integrity impact was observed.

Are you affected?

You are affected if your application uses pyasn1 0.3.3 or later but below 0.6.5 and passes attacker-controlled bytes to schemaless BER, CER, or DER decoding.

Package / productAffected versionsFixed in
pyasn1 · pip>= 0.3.3, < 0.6.50.6.5

What to do

  1. Upgrade pyasn1 to version 0.6.5 or later (pip install --upgrade pyasn1)
  2. If upgrading is not possible now, avoid decoding untrusted BER, CER, or DER data without a schema
  3. Check your dependency lock files to confirm pyasn1 is at 0.6.5 or later

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-2026-119194 · GHSA-fm9c-5rcf-2q5p
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 decoder can be slowed to a crawl by crafted input · Zero Radar