CVE-2026-48523Public exploitNetwork attack vector

Authentication policy bypass via mismatched verification algorithm

Published May 28, 2026 · Updated May 28, 2026

Improper signature verification in PyJWT 2.9.0 through 2.12.1 allows remote authenticated users to bypass JWT algorithm policy. In jwt/api_jws.py, _verify_signature() checks the token header algorithm against the allow-list but verifies with the algorithm bound to the PyJWK key. Exploitation requires control of an accepted JWK/JWKS private key and permits authentication as that registered principal with a blocked algorithm, not keyless forgery or cross-tenant impersonation.

CVSS severity5.4
Medium
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper signature verification in PyJWT 2.9.0 through 2.12.1 allows remote authenticated users to bypass JWT algorithm policy. In jwt/api_jws.py, _verify_signature() checks the token header algorithm against the allow-list but verifies with the algorithm bound to the PyJWK key. Exploitation requires control of an accepted JWK/JWKS private key and permits authentication as that registered principal with a blocked algorithm, not keyless forgery or cross-tenant impersonation.

The record

CVE
CVE-2026-48523
Published
May 28, 2026
Updated
May 28, 2026
Vendor
Jose Padilla
Product
PyJWT
Classifications
CWE-347, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 28, 2026CVE publishedPublication date reported by the CVE source.
  2. May 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2.9.0, < 2.13.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Jose Padilla · PyJWTversion=>= 2.9.0, < 2.13.0

Published CVSS scores

5.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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