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Pyasn1Application

CVE-2026-59884

HIGH · 7.5 CVSS v3.1 Published 2026-07-14
Fix available
A fix is available. Upgrade to 0.6.4 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click 5 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The BER decoder in pyasn1 versions prior to 0.6.4 parses long-form ASN.1 tags without imposing an upper bound on tag ID size, allowing attackers to craft input that forces construction of arbitrarily large integers with quadratic CPU cost growth. Additionally, the vulnerability triggers unhandled ValueError exceptions in Python 3.11+ error formatting paths.

MitigationUpgrade pyasn1 to version 0.6.4 or later. If immediate upgrading is not feasible, ensure untrusted BER, CER, or DER input is not processed by vulnerable versions.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Pyasn1Application
Affected:< 0.6.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed pyasn1 version
    Run 'pip show pyasn1' or 'python -c "import pyasn1; print(pyasn1.__version__)"' to get the installed version number
    Affected if The version shown is less than 0.6.4 or no version is displayed (indicating an unpatched installation)
  2. Verify BER/CER/DER decoding is in use
    Search codebases for imports of 'pyasn1.codec.ber' or 'pyasn1.codec.cer' or 'pyasn1.codec.der' and their decoder modules (e.g., 'from pyasn1.codec.ber import decoder')
    Affected if These decoder modules are imported and used to process external ASN.1 input
  3. Check for long-form ASN.1 tag handling
    Inspect network traffic logs, file imports, or application inputs that feed BER/CER/DER data to pyasn1 for any unusually large tag identifiers in the ASN.1 structure
    Affected if Large or malformed ASN.1 tags (multi-byte tag IDs) are being processed by the decoder
  4. Confirm Python runtime version
    Run 'python --version' or 'python3 --version' to determine the Python interpreter version
    Affected if Python 3.11 or newer is in use, which exposes the secondary ValueError error-formatting issue

The environment is affected if pyasn1 version is below 0.6.4 AND the BER/CER/DER decoder is processing untrusted ASN.1 input, especially when running on Python 3.11+.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.6.4 or later
Fixed in 0.6.4
Interim mitigation

Upgrade pyasn1 to version 0.6.4 or later. If immediate upgrading is not feasible, ensure untrusted BER, CER, or DER input is not processed by vulnerable versions.

Recommended fix High confidence

pyasn1 version 0.6.4 or later

  1. Identify all Python project dependencies that include pyasn1 (e.g., check requirements.txt, setup.py, pyproject.toml, or pip freeze output)
  2. Upgrade pyasn1 to version 0.6.4 or later using: pip install --upgrade pyasn1>=0.6.4
  3. Verify the installed version matches the requirement: pip show pyasn1
  4. Rebuild and redeploy any applications or containers that depend on the updated library
  5. Test that ASN.1 decoding functionality (BER, CER, DER) continues to work correctly with the updated library

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Pyasn1 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,900
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-59884 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data