CVE-2026-102273

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWT HMACAlgorithm.prepare_key is affected because HMAC key guard only recognizes top-level public JWK forms and misses container representations. This occurs when an application allows HMAC and asymmetric algorithms and passes a public JWK container as the raw key. As a result, public asymmetric key material is accepted as the HMAC secret. Consequently, an attacker who knows the public key can forge a token with arbitrary authenticated claims. This issue is fixed in version 2.14.0.

Summary

PyJWT 2.13.0 contains an incomplete defense against algorithm confusion when an application mixes symmetric and asymmetric algorithms in one verification path. A public RSA, EC, or OKP JWK can be accepted as an HMAC secret when it is wrapped in a JWKS object, nested in an array, or represented in another container form that does not expose a top-level kty member.

Impact

An attacker who knows the public key material can forge HS256/HS384/HS512 tokens if the application simultaneously:

• allows both HS* and asymmetric algorithms;
• passes raw public JWK/JWKS JSON as key=; and
• uses that same value as the HMAC secret.

This can allow forged JWT claims in affected application configurations. The issue does not affect applications that keep symmetric and asymmetric verification paths separate and follow PyJWT's algorithm-selection guidance.

Fix status

The fix is on master in commit 801cd12 (fix: reject public JWK container HMAC keys). HMACAlgorithm.prepare_key now rejects public JWK members found in objects, arrays, nested containers, BOM/UTF variants, and recursion-limit inputs. It also recognizes escaped JSON member names without treating ordinary string values as JWKs. Ordinary JSON secrets remain accepted byte-for-byte.

The change was tested with focused regression tests and the full local tox matrix. Available Python 3.9, 3.12, and 3.13 crypto/no-crypto suites, mypy, package metadata, and coverage passed; unavailable interpreters were skipped by the project configuration. A fresh independent Astra/max security review accepted the final diff with no blocking findings.

The affected range is = 2.13.0. The fix is on the unreleased development branch; the patched version will be recorded when a released 2.x version containing the fix is available. This advisory is being moved to draft pending that release.

Reporter credit

Credit: Charles Vosburgh / Trilobyte.

Original report

The original report and reproduction package are retained in the private advisory record.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

Summary

PyJWT 2.13.0 contains an incomplete defense against algorithm confusion when an application mixes symmetric and asymmetric algorithms in one verification path. A public RSA, EC, or OKP JWK can be accepted as an HMAC secret when it is wrapped in a JWKS object, nested in an array, or represented in another container form that does not expose a top-level kty member.

Impact

An attacker who knows the public key material can forge HS256/HS384/HS512 tokens if the application simultaneously:

• allows both HS* and asymmetric algorithms;
• passes raw public JWK/JWKS JSON as key=; and
• uses that same value as the HMAC secret.

This can allow forged JWT claims in affected application configurations. The issue does not affect applications that keep symmetric and asymmetric verification paths separate and follow PyJWT's algorithm-selection guidance.

Fix status

The fix is on master in commit 801cd12 (fix: reject public JWK container HMAC keys). HMACAlgorithm.prepare_key now rejects public JWK members found in objects, arrays, nested containers, BOM/UTF variants, and recursion-limit inputs. It also recognizes escaped JSON member names without treating ordinary string values as JWKs. Ordinary JSON secrets remain accepted byte-for-byte.

The change was tested with focused regression tests and the full local tox matrix. Available Python 3.9, 3.12, and 3.13 crypto/no-crypto suites, mypy, package metadata, and coverage passed; unavailable interpreters were skipped by the project configuration. A fresh independent Astra/max security review accepted the final diff with no blocking findings.

The affected range is = 2.13.0. The fix is on the unreleased development branch; the patched version will be recorded when a released 2.x version containing the fix is available. This advisory is being moved to draft pending that release.

Reporter credit

Credit: Charles Vosburgh / Trilobyte.

Original report

The original report and reproduction package are retained in the private advisory record.

Maintainer update — 2026-09-11

The verified fix for this advisory is included in PyJWT 2.14.0, released on 2026-09-11 and available on PyPI. PyJWT 2.14.0 is the first release containing the fix. This advisory is now published with 2.14.0 recorded as the patched version.

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWT HMACAlgorithm.prepare_key is affected because HMAC key guard only recognizes top-level public JWK forms and misses container representations. This occurs when an application allows HMAC and asymmetric algorithms and passes a public JWK container as the raw key. As a result, public asymmetric key material is accepted as the HMAC secret. Consequently, an attacker who knows the public key can forge a token with arbitrary authenticated claims. This issue is fixed in version 2.14.0.

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWT HMACAlgorithm.prepare_key is affected because HMAC key guard only recognizes top-level public JWK forms and misses container representations. This occurs when an application allows HMAC and asymmetric algorithms and passes a public JWK container as the raw key. As a result, public asymmetric key material is accepted as the HMAC secret. Consequently, an attacker who knows the public key can forge a token with arbitrary authenticated claims. This issue is fixed in version 2.14.0.

TuxCare rebuilt pyjwt to address 3 CVEs. Fixed in 2.10.1.post8+tuxcare.

TuxCare rebuilt pyjwt to address 4 CVEs. Fixed in 2.8.0.post6+tuxcare.

TuxCare rebuilt pyjwt to address 3 CVEs. Fixed in 2.3.0.post6+tuxcare.

Root has patched CVE-2026-102273 in the pyjwt package for Root:PyPI. Multiple fixed versions available.

YuSung Han discovered that PyJWT did not properly validate certain JWK keys when performing HMAC verification. An attacker could possibly use this issue to forge authentication tokens. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-102266)

Rohan Das discovered that PyJWT incorrectly handled redirects when fetching key sets. A remote attacker could possibly use this issue to cause PyJWT to disclose sensitive information. This issue only affected Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 26.04 LTS. (CVE-2026-102267)

It was discovered that PyJWT incorrectly recognized certain PEM representations. An attacker who knew the public key could possibly use this issue to forge authentication tokens. This issue only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 26.04 LTS. (CVE-2026-102268)

Nuno Lopes discovered that PyJWT incorrectly handled DER public keys when performing HMAC verification. An attacker who knew the public key could possibly use this issue to forge authentication tokens. (CVE-2026-102271)

It was discovered that PyJWT did not properly handle certain JWK keys prefixed with a byte-order mark. An attacker who knew the public key could possibly use this issue to forge authentication tokens. (CVE-2026-102272)

Charles Vosburgh discovered that PyJWT incorrectly handled certain JWK containers when performing HMAC verification. An attacker who knew the public key could possibly use this issue to forge authentication tokens. (CVE-2026-102273)

USN-8916-1 fixed vulnerabilities in PyJWT. This update provides the corresponding fix for PyJWT on Ubuntu 26.10.

Original advisory details:

YuSung Han discovered that PyJWT did not properly validate certain JWK keys when performing HMAC verification. An attacker could possibly use this issue to forge authentication tokens. (CVE-2026-102266)

Rohan Das discovered that PyJWT incorrectly handled redirects when fetching key sets. A remote attacker could possibly use this issue to cause PyJWT to disclose sensitive information. (CVE-2026-102267)

It was discovered that PyJWT incorrectly recognized certain PEM representations. An attacker who knew the public key could possibly use this issue to forge authentication tokens. (CVE-2026-102268)

Nuno Lopes discovered that PyJWT incorrectly handled DER public keys when performing HMAC verification. An attacker who knew the public key could possibly use this issue to forge authentication tokens. (CVE-2026-102271)

It was discovered that PyJWT did not properly handle certain JWK keys prefixed with a byte-order mark. An attacker who knew the public key could possibly use this issue to forge authentication tokens. (CVE-2026-102272)

Charles Vosburgh discovered that PyJWT incorrectly handled certain JWK containers when performing HMAC verification. An attacker who knew the public key could possibly use this issue to forge authentication tokens. (CVE-2026-102273)