CriticalCVE-2026-102266

    PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation (CVE-2026-102266)

    Published Last modified Sources: Red Hat, Ubuntu, BSI, OSV, Hersteller, CVE.org, Msrc Update Guide

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    What is affected, what to do

    A flaw was found in pyjwt. A remote attacker can forge authentication tokens and bypass security controls by signing tokens with an empty key.

    The available sources name no fixed version. Check the vendor guidance in the references below.

    Affected
    • Jpadilla Pyjwt gte 2.13.0, < 2.14.0..*

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.1

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.4

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Red Hat, Ubuntu, BSI, OSV, Hersteller, CVE.org, Msrc Update Guide

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 13.3

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    67.18 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.1 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.4
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

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    0.2 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    13.3
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: proof of concept · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 29 September 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-347

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A flaw was found in pyjwt. A remote attacker can forge authentication tokens and bypass security controls by signing tokens with an empty key. When verifying tokens against a JSON Web Key (JWK) set that contains an empty Hash-based Message Authentication Code (HMAC) key, the library fails to enforce key-length validation. This allows an attacker to generate valid tokens carrying arbitrary claims to gain unauthorized access.

    Source: redhat_csaf, Ubuntu Security Notices, BSI WID Portal, BSI CSAF, OSV (Open Source Vulnerabilities), GitHub Security Advisories, NVD (NIST), cvelistv5, Microsoft Security Update Guide

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    jpadillapyjwt
    • ≥ 2.13.0, < 2.14.0
    • —
    pyjwt_projectpyjwt
    • 2.13.0
    • —
    Red HatAnsible Automation Platform
    • 2.6
    • 2.7
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxubuntupyjwtbionic
    Linuxubuntupyjwtfocal
    Linuxubuntupyjwtjammy
    Linuxubuntupyjwtnoble
    Linuxubuntupyjwtresolute
    Linuxubuntupyjwtstonking
    Linuxubuntupyjwtxenial

    Weakness classes (CWE)

    • CWE-347Improper Verification of Cryptographic Signature

      Base

      The product does not verify, or incorrectly verifies, the cryptographic signature for data.

      Entry at MITRE CWE-347

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Initial analysis by NVDNVD

      Newly listed as affected:

      CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
      Product configurationadded
      —
      OR *cpe:2.3:a:pyjwt_project:pyjwt:2.13.0:*:*:*:*:*:*:*
      Reference typeadded
      —
      GitHub, Inc.: https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c Types: Patch
      Reference typeadded
      —
      GitHub, Inc.: https://github.com/jpadilla/pyjwt/releases/tag/2.14.0 Types: Product, Release Notes
      Reference typeadded
      —
      CISA-ADP: https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r Types: Exploit, Vendor Advisory
      Reference typeadded
      —
      GitHub, Inc.: https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r Types: Exploit, Vendor Advisory

      Source identifier: nvd@nist.gov

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: proof of concept, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r
      SSVC assessmentadded
      —
      {"id":"CVE-2026-102266","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-29T19:28:36.086597Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    3. ReceivedGitHub

      CVSS V3.1: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

      Weakness type: CWE-347

      Description added or changed

      Show 7 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.from_jwk is affected because PyJWK verification path used the decoded key without applying prepare_key validation. This occurs when a trusted JWK Set contains an oct entry with an empty k value. As a result, an attacker signs an HMAC token with the same zero-length key accepted by PyJWT. Consequently, forged token can carry arbitrary authenticated claims. This issue is fixed in version 2.14.0.
      CVSSadded
      —
      AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
      Weakness type (CWE)added
      —
      CWE-347
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/102xxx/CVE-2026-102266.json">CVE-2026-102266</a>
      Referenceadded
      —
      https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c
      Referenceadded
      —
      https://github.com/jpadilla/pyjwt/releases/tag/2.14.0
      Referenceadded
      —
      https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r

      Source identifier: security-advisories@github.com

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