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PyJWT CVE-2026-102266

| EUVDEUVD-2026-88484 CRITICAL
Improper Verification of Cryptographic Signature (CWE-347)
2026-09-28 GitHub_M GHSA-9j54-fg26-wv3r
Python Jwt Attack Pyjwt Jpadilla
9.1
CVSS 3.1 · NVD
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Severity by source

Vendor (GitHub_M) PRIMARY
HIGH
qualitative
NVD
9.1 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
vuln.today AI
7.4 HIGH

No auth needed (PR:N), but exploitation depends on a pre-existing empty oct JWK beyond attacker control, so AC:H; token forgery breaks confidentiality and integrity, not availability (A:N).

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
7.4 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat
7.4 HIGH
qualitative

Primary rating from Vendor (GitHub_M).

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

9
Analysis Updated
Oct 07, 2026 - 21:13 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Oct 07, 2026 - 21:07 vuln.today
cvss_changed
Severity Changed
Oct 07, 2026 - 21:07 NVD
HIGH CRITICAL
CVSS changed
Oct 07, 2026 - 21:07 NVD
7.4 (HIGH) 9.1 (CRITICAL)
POC Analysis Generated
Sep 28, 2026 - 23:25 vuln.today
Metadata Corrected
Sep 28, 2026 - 21:40 vuln.today
tag: RCE removed
Patch available
Sep 28, 2026 - 21:02 EUVD
Analysis Generated
Sep 28, 2026 - 20:48 vuln.today
CVE Published
Sep 28, 2026 - 20:21 cve.org
HIGH 7.4

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 206 pypi packages depend on pyjwt (131 direct, 76 indirect)

Ecosystem-wide dependent count for version 2.13.0.

DescriptionNVD

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.

Articles & Coverage 1

News 13 New Python Vulnerabilities - 2 Critical, 11 High, 2 With POC Sep 29, 2026

AnalysisAI

Forged HS256 JSON Web Tokens can be accepted as authentic by PyJWT (pip package PyJWT) versions 2.13.0 through 2.13.x when an application verifies tokens through the PyJWK or PyJWKSet path and its trusted JWK Set already contains a symmetric oct entry with an empty key value ({"kty":"oct","k":""}), an unusual precondition typically caused by a missing Base64URL configuration or secret-manager value. Because the PyJWK verification path passes the decoded zero-length key straight to the HMAC check instead of running it through HMACAlgorithm.prepare_key, unauthenticated remote attackers (CVSS PR:N) who know this pre-existing misconfiguration can independently compute HMAC-SHA256(b"", signing_input) and mint valid tokens carrying arbitrary authenticated claims, giving high confidentiality and integrity impact. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
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Exploit
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Execution
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Impact
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Vulnerability AssessmentAI

Exploitation Exploitable only when the service verifies HS256 tokens via the PyJWK/PyJWKSet path AND its trusted JWK Set already contains an oct entry with an empty k value ({"kty":"oct","k":""}), which decodes to b"" - typically arising when a missing Base64URL config or secret-manager value is serialized as "k":"". … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment Signals conflict sharply, so the headline CVSS 9.1 overstates real-world urgency. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade PyJWT to the vendor-released patch version 2.14.0 (pip install -U PyJWT), which routes JWK-sourced HMAC keys through HMACAlgorithm.prepare_key and rejects empty keys with InvalidKeyError, per the fix commit f91ed44dd65baaf457f4b3353ed35e98a753934c and release notes at https://github.com/jpadilla/pyjwt/releases/tag/2.14.0. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, inventory all applications and services that use PyJWT versions 2.13.0 through 2.13.x and determine whether they verify tokens through the PyJWK or PyJWKSet path with a symmetric oct key entry that may be empty. …

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Same weakness CWE-347 – Improper Verification of Cryptographic Signature

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 12 Not-Affected
SUSE Linux Enterprise Micro 5.5 Not-Affected
SUSE Linux Enterprise Module for Basesystem 15 SP7 Not-Affected
SUSE Linux Enterprise Module for Python 3 15 SP7 Not-Affected

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CVE-2026-102266 vulnerability details – vuln.today
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