CVE-2026-85394: Python jose Python-jose Algorithm Confusion Guard Bypassed Vulnerability

CRITICAL
Advisory Identifier: GHSA-3qf3-8w2g-rqmx
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CVSS 9.1
CWE-347
Published
Advisory Summary

CVE-2026-85394 is a CRITICAL (CVSS 9.1) python-jose algorithm confusion guard bypassed vulnerability (CWE-347: Improper Verification of Cryptographic Signature) affecting Python jose libraries in the PyPI ecosystem. The issue involves python-jose algorithm confusion guard bypassed by der-encoded public keys. Remediation is available in the latest vendor maintenance releases.

CVE-2026-85394 at a Glance

CVE Identifier CVE-2026-85394
GHSA Identifier GHSA-3qf3-8w2g-rqmx
Severity CRITICAL
CVSS v3.1 Base Score 9.1
CWE Classification CWE-347: Improper Verification of Cryptographic Signature
Affected Product Python jose
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 9.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-85394

To remediate this vulnerability, upgrade all affected Python jose dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

python-jose fixed: Latest secure release 
pip install python-jose>=Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show python-jose

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-85394, inspect your installed packages using pip:

pip show python-jose

Analyze the terminal output to locate any version of Python jose in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The pip show python-jose command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-347: Improper Verification of Cryptographic Signature, where the product does not verify, or incorrectly verifies, the cryptographic signature for data. In Python jose, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

python-jose through 3.5.0 fails to properly validate asymmetric keys in HMAC initialization, accepting DER-encoded public keys that lack PEM armor or SSH prefixes. Attackers holding the service's public key can forge HS256 tokens that pass verification when algorithms are not explicitly restricted. This is an incomplete fix for CVE-2024-33663.

CVE-2026-85394 Affected Python jose Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
python-jose
pypi/python-jose
PyPI
≤ 3.5.0

References

NVD — CVE-2026-85394 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-85394
Python jose Source Repository REPOSITORY
https://github.com/mpdavis/python-jose/issues/414
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-6c5p-j8vq-pqhj
Python jose Source Repository REPOSITORY
https://github.com/mpdavis/python-jose
Python jose Source Repository REPOSITORY
https://github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jose/backends/native.py
Python jose Source Repository REPOSITORY
https://github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jose/utils.py
www.vulncheck.com/advisories/python-j... WEB
https://www.vulncheck.com/advisories/python-jose-through-3.5.0-algorithm-confusion-via-der-encoded-public-key-as-hmac-secret

Frequently Asked Questions

What is CVE-2026-85394?
CVE-2026-85394 is a security vulnerability in Python jose involving python-jose algorithm confusion guard bypassed by DER-encoded public keys under CWE-347: Improper Verification of Cryptographic Signature.
Which Python jose versions are affected?
Affected versions include releases prior to current release patches across affected packages: python-jose.
What version fixes CVE-2026-85394?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is python-jose affected?
Yes, python-jose is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2026-85394?
CVE-2026-85394 has a CVSS v3.1 base score of 9.1 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
What CWE is associated with CVE-2026-85394?
CVE-2026-85394 is classified under CWE-347: Improper Verification of Cryptographic Signature (The product does not verify, or incorrectly verifies, the cryptographic signature for data.).
How can I check PyPI dependencies for CVE-2026-85394?
Run the dependency tree command: 'pip show python-jose'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3qf3-8w2g-rqmx",
  "modified" : "2026-10-05T22:55:01Z",
  "published" : "2026-09-03T21:31:15Z",
  "aliases" : [ "CVE-2026-85394" ],
  "summary" : "python-jose algorithm confusion guard bypassed by DER-encoded public keys",
  "details" : "python-jose through 3.5.0 fails to properly validate asymmetric keys in HMAC initialization, accepting DER-encoded public keys that lack PEM armor or SSH prefixes. Attackers holding the service's public key can forge HS256 tokens that pass verification when algorithms are not explicitly restricted. This is an incomplete fix for CVE-2024-33663.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
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    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
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      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
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  }, {
    "type" : "WEB",
    "url" : "https://github.com/mpdavis/python-jose/issues/414"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-6c5p-j8vq-pqhj"
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  }, {
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    "url" : "https://github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jose/utils.py"
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    "type" : "WEB",
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  } ],
  "database_specific" : {
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    "github_reviewed_at" : "2026-10-05T22:55:01Z",
    "nvd_published_at" : "2026-09-03T19:17:31Z"
  }
}