REDHAT-BUG-2542687: High severity pypi/pyjwt vulnerability

Q: Which deployments are exposed to token forgery?

Deployments are exposed if they use PyJWT from 2.4.0 through 2.14.0, allow both HMAC and asymmetric algorithms, and provide an asymmetric public key in DER format as the shared verification key. The issue does not follow from using PyJWT alone; this algorithm and key-handling combination is required.

Q: What does an attacker need to exploit this issue?

The attacker needs to know the public key used by the application. Under the affected configuration, they can use the public DER key bytes as an HMAC secret to forge tokens accepted as authenticated.

Q: How can the issue be remediated?

Update PyJWT to version 2.14.0, which fixes the issue. If updating is not immediately possible, avoid mixing HMAC and asymmetric algorithms and do not use a DER-encoded public key as a shared verification key.

Published Sep 28, 2026

Updated

PyJWT is a Python implementation of JSON Web Token standards. From 2.4.0 until 2.14.0, PyJWT HMACAlgorithm.preparekey is affected because asymmetric-key guard relies on textual markers that are absent from DER encoding. This occurs when an application mixes HMAC and asymmetric algorithms and supplies a DER public key as the shared verification key. As a result, PyJWT uses public DER bytes as an HMAC secret. Consequently, an attacker who knows the public key can forge authenticated HMAC tokens. This issue is fixed in version 2.14.0.

Affected Software

1 affected component

pypi/pyjwt>=2.4.0<2.14.0

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
Upgrade PyJWT to a version that resolves this vulnerability.
Fixed in 2.14.0

Event History

Sep 28, 2026

Data Sourced

via Red Hat·08:46 PM

DescriptionSeverityAffected Software

Frequently Asked Questions

Which deployments are exposed to token forgery?

Deployments are exposed if they use PyJWT from 2.4.0 through 2.14.0, allow both HMAC and asymmetric algorithms, and provide an asymmetric public key in DER format as the shared verification key. The issue does not follow from using PyJWT alone; this algorithm and key-handling combination is required.

What does an attacker need to exploit this issue?

The attacker needs to know the public key used by the application. Under the affected configuration, they can use the public DER key bytes as an HMAC secret to forge tokens accepted as authenticated.

How can the issue be remediated?

Update PyJWT to version 2.14.0, which fixes the issue. If updating is not immediately possible, avoid mixing HMAC and asymmetric algorithms and do not use a DER-encoded public key as a shared verification key.

REDHAT-BUG-2542687: High severity pypi/pyjwt vulnerability

Affected Software

Remediation

Event History

Frequently Asked Questions

Which deployments are exposed to token forgery?

What does an attacker need to exploit this issue?

How can the issue be remediated?

Company

Resources

Contact

Frequently Asked Questions

Which deployments are exposed to token forgery?

What does an attacker need to exploit this issue?

How can the issue be remediated?