CVE-2026-101917

In PyJWT versions 1.5.0 and below, the `invalid_strings` check in `HMACAlgorithm.prepare_key` does not account for all PEM encoded public keys. Specifically, the PKCS1 PEM encoded format is allowed, enabling symmetric/asymmetric key confusion attacks.

PyJWT is a Python implementation of JSON Web Token standards. Prior to version 2.14.0, is_pem_format in jwt/utils.py does not recognize every PEM representation accepted by the cryptography loader. When an application mixes HMAC and asymmetric algorithms and supplies a mutated public-key PEM as raw key bytes, HMACAlgorithm.prepare_key treats the unrecognized asymmetric public key as an HMAC secret. An attacker who knows the public key can forge authenticated HMAC tokens. This issue is fixed in version 2.14.0.

PyJWT is a Python implementation of JSON Web Token standards. From 2.11.0 through 2.13.0, PyJWT._merge_options() can modify a caller-supplied mutable options mapping when verify_signature is false. If an application reuses that same mapping for a later decode() or decode_complete() call and changes verify_signature to true, the mapping can retain false values for expiration, not-before, issued-at, audience, issuer, subject, and JWT ID checks, allowing a signed token with invalid registered claims to be accepted without disabling signature verification; applications that create a fresh options mapping for each call are not affected.

PyJWT is a Python implementation of JSON Web Token standards. From 2.1.0 until 2.15.0, PyJWT OKPAlgorithm.from_jwk in jwt/algorithms.py is affected because private-JWK import path does not compare the public key derived from d with x. This occurs when an OKP private JWK supplies non-corresponding x and d components. As a result, identity derived from x can differ from operations performed with d.

PyJWT is a Python implementation of JSON Web Token standards. From 2.9.0 until 2.14.0, PyJWKSet does not catch the plain ValueError raised for malformed RSA JWK components by RSAAlgorithm.from_jwk in jwt/api_jwk.py. This occurs when a JWK Set contains a malformed RSA key alongside otherwise usable keys. As a result, one malformed member aborts construction of the entire PyJWKSet.

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.prepare_key is affected because the HMAC key guard only recognizes top-level public JWK forms and misses container representations. When an application allows HMAC and asymmetric algorithms and passes a public JWK container as the raw key, 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.

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.prepare_key in jwt/algorithms.py is affected because the raw-JWK detector does not normalize accepted Unicode byte-order marks before checking for JSON. When a public JWK is prefixed with a UTF-8 BOM and used in a mixed-algorithm verification path, the public JWK bypasses asymmetric-key detection and becomes the HMAC secret. Consequently, an attacker who knows the public key can forge authenticated tokens.

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

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT is_pem_format is affected because lazy PEM regular expression backtracks extensively. This occurs when a certificate-like input contains repeated BEGIN markers without a matching END marker. As a result, is_pem_format performs unbounded backtracking while searching for a PEM end marker.

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments.