CVE-2026-32597

PyJWT is a JSON Web Token implementation in Python. Prior to 2.12.0, PyJWT does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that PyJWT does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC. This vulnerability is fixed in 2.12.0.

Summary

PyJWT does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that PyJWT does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC.

This is the same class of vulnerability as CVE-2025-59420 (Authlib), which received CVSS 7.5 (HIGH).

RFC Requirement

RFC 7515 §4.1.11:

The "crit" (Critical) Header Parameter indicates that extensions to this specification and/or [JWA] are being used that MUST be understood and processed. [...] If any of the listed extension Header Parameters are not understood and supported by the recipient, then the JWS is invalid.

Proof of Concept

import jwt  # PyJWT 2.8.0
import hmac, hashlib, base64, json

# Construct token with unknown critical extension
header = {"alg": "HS256", "crit": ["x-custom-policy"], "x-custom-policy": "require-mfa"}
payload = {"sub": "attacker", "role": "admin"}

def b64url(data):
    return base64.urlsafe_b64encode(data).rstrip(b"=").decode()

h = b64url(json.dumps(header, separators=(",", ":")).encode())
p = b64url(json.dumps(payload, separators=(",", ":")).encode())
sig = b64url(hmac.new(b"secret", f"{h}.{p}".encode(), hashlib.sha256).digest())
token = f"{h}.{p}.{sig}"

# Should REJECT — x-custom-policy is not understood by PyJWT
try:
    result = jwt.decode(token, "secret", algorithms=["HS256"])
    print(f"ACCEPTED: {result}")
    # Output: ACCEPTED: {'sub': 'attacker', 'role': 'admin'}
except Exception as e:
    print(f"REJECTED: {e}")

Expected: jwt.exceptions.InvalidTokenError: Unsupported critical extension: x-custom-policy Actual: Token accepted, payload returned.

Comparison with RFC-compliant library

# jwcrypto — correctly rejects
from jwcrypto import jwt as jw_jwt, jwk
key = jwk.JWK(kty="oct", k=b64url(b"secret"))
jw_jwt.JWT(jwt=token, key=key, algs=["HS256"])
# raises: InvalidJWSObject('Unknown critical header: "x-custom-policy"')

Impact

• Split-brain verification in mixed-library deployments (e.g., API gateway using jwcrypto rejects, backend using PyJWT accepts)
• Security policy bypass when crit carries enforcement semantics (MFA, token binding, scope restrictions)
• Token binding bypass — RFC 7800 cnf (Proof-of-Possession) can be silently ignored
• See CVE-2025-59420 for full impact analysis

Suggested Fix

In jwt/api_jwt.py, add validation in _validate_headers() or decode():

_SUPPORTED_CRIT = {"b64"}  # Add extensions PyJWT actually supports

def _validate_crit(self, headers: dict) -> None:
    crit = headers.get("crit")
    if crit is None:
        return
    if not isinstance(crit, list) or len(crit) == 0:
        raise InvalidTokenError("crit must be a non-empty array")
    for ext in crit:
        if ext not in self._SUPPORTED_CRIT:
            raise InvalidTokenError(f"Unsupported critical extension: {ext}")
        if ext not in headers:
            raise InvalidTokenError(f"Critical extension {ext} not in header")

CWE

• CWE-345: Insufficient Verification of Data Authenticity
• CWE-863: Incorrect Authorization

References

• RFC 7515 §4.1.11
• CVE-2025-59420 — Authlib crit bypass (CVSS 7.5)
• RFC 7800 — Proof-of-Possession Key Semantics

rm -f tests/test_jwks_client.py -m pytest %endif

Security Fix(es):

PyJWT is a JSON Web Token implementation in Python. Prior to 2.12.0, PyJWT does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that PyJWT does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC. This vulnerability is fixed in 2.12.0.(CVE-2026-32597)

PyJWT is a JSON Web Token implementation in Python. Prior to 2.12.0, PyJWT does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that PyJWT does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC. This vulnerability is fixed in 2.12.0.

The fence-agents packages provide a collection of scripts for handling remote power management for cluster devices. They allow failed or unreachable nodes to be forcibly restarted and removed from the cluster.

Security Fix(es):

• cryptography: cryptography Subgroup Attack Due to Missing Subgroup Validation for SECT Curves (CVE-2026-26007)

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)

• pyasn1: pyasn1 Vulnerable to Denial of Service via Unbounded Recursion (CVE-2026-30922)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The fence-agents packages provide a collection of scripts for handling remote power management for cluster devices. They allow failed or unreachable nodes to be forcibly restarted and removed from the cluster.

Security Fix(es):

• cryptography: cryptography Subgroup Attack Due to Missing Subgroup Validation for SECT Curves (CVE-2026-26007)

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The fence-agents packages provide a collection of scripts for handling remote power management for cluster devices. They allow failed or unreachable nodes to be forcibly restarted and removed from the cluster.

Security Fix(es):

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)

• pyasn1: pyasn1 Vulnerable to Denial of Service via Unbounded Recursion (CVE-2026-30922)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The fence-agents packages provide a collection of scripts for handling remote power management for cluster devices. They allow failed or unreachable nodes to be forcibly restarted and removed from the cluster.

Security Fix(es):

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)

• pyasn1: pyasn1 Vulnerable to Denial of Service via Unbounded Recursion (CVE-2026-30922)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The fence-agents packages provide a collection of scripts for handling remote power management for cluster devices. They allow failed or unreachable nodes to be forcibly restarted and removed from the cluster.

Security Fix(es):

• cryptography: cryptography Subgroup Attack Due to Missing Subgroup Validation for SECT Curves (CVE-2026-26007)

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)

• pyasn1: pyasn1 Vulnerable to Denial of Service via Unbounded Recursion (CVE-2026-30922)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Root has patched CVE-2026-32597 in the PyJWT package for Root:PyPI. Multiple fixed versions available.

PyJWT is a JSON Web Token implementation in Python. Prior to 2.12.0, PyJWT does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that PyJWT does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC. This vulnerability is fixed in 2.12.0.

The fence-agents packages provide a collection of scripts for handling remote power management for cluster devices. They allow failed or unreachable nodes to be forcibly restarted and removed from the cluster.

Security Fix(es):

• cryptography: cryptography Subgroup Attack Due to Missing Subgroup Validation for SECT Curves (CVE-2026-26007)
• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)
• pyasn1: pyasn1 Vulnerable to Denial of Service via Unbounded Recursion (CVE-2026-30922)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The fence-agents packages provide a collection of scripts for handling remote power management for cluster devices. They allow failed or unreachable nodes to be forcibly restarted and removed from the cluster.

Security Fix(es):

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)
• pyasn1: pyasn1 Vulnerable to Denial of Service via Unbounded Recursion (CVE-2026-30922)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• pyjwt: PyJWT accepts unknown crit header extensions (RFC 7515 ?4.1.11 MUST violation) (CVE-2026-32597)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

PyJWT is a JSON Web Token implementation in Python. Prior to 2.12.0, PyJWT does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that PyJWT does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC. This vulnerability is fixed in 2.12.0.

TuxCare rebuilt pyjwt to address 1 CVE. Fixed in 1.7.1.post2+tuxcare.

TuxCare rebuilt pyjwt to address 1 CVE. Fixed in 2.10.1.post3+tuxcare.

TuxCare rebuilt pyjwt to address 2 CVEs. Fixed in 2.8.0.post3+tuxcare.

TuxCare rebuilt pyjwt to address 1 CVE. Fixed in 2.3.0.post3+tuxcare.

These are all security issues fixed in the python311-PyJWT-2.12.1-1.1 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the python311-social-auth-core-4.8.7-1.1 package on the GA media of openSUSE Tumbleweed.

This update for python-PyJWT fixes the following issue:

Update to PyJWT 2.12.1:

• CVE-2026-32597: PyJWT accepts unknown crit header extensions (bsc#1259616).

Changelog:

Update to 2.12.1:

• Add missing typing_extensions dependency for Python < 3.11 in #1150

Update to 2.12.0:

• Annotate PyJWKSet.keys for pyright by @tamird in #1134
• Close HTTPError response to prevent ResourceWarning on Python 3.14 by @veeceey in #1133
• Do not keep algorithms dict in PyJWK instances by @akx in #1143
• Use PyJWK algorithm when encoding without explicit algorithm in #1148
• Docs: Add PyJWKClient API reference and document the two-tier caching system (JWK Set cache and signing key LRU cache).

Update to 2.11.0:

• Enforce ECDSA curve validation per RFC 7518 Section 3.4.
• Fix build system warnings by @kurtmckee in #1105
• Validate key against allowed types for Algorithm family in #964
• Add iterator for JWKSet in #1041
• Validate iss claim is a string during encoding and decoding by @pachewise in #1040
• Improve typing/logic for options in decode, decode_complete by @pachewise in #1045
• Declare float supported type for lifespan and timeout by @nikitagashkov in #1068
• Fix SyntaxWarnings/DeprecationWarnings caused by invalid escape sequences by @kurtmckee in #1103
• Development: Build a shared wheel once to speed up test suite setup times by @kurtmckee in #1114
• Development: Test type annotations across all supported Python versions, increase the strictness of the type checking, and remove the mypy pre-commit hook by @kurtmckee in #1112
• Support Python 3.14, and test against PyPy 3.10 and 3.11 by @kurtmckee in #1104
• Development: Migrate to build to test package building in CI by @kurtmckee in #1108
• Development: Improve coverage config and eliminate unused test suite code by @kurtmckee in #1115
• Docs: Standardize CHANGELOG links to PRs by @kurtmckee in #1110
• Docs: Fix Read the Docs builds by @kurtmckee in #1111
• Docs: Add example of using leeway with nbf by @djw8605 in #1034
• Docs: Refactored docs with autodoc; added PyJWS and jwt.algorithms docs by @pachewise in #1045
• Docs: Documentation improvements for "sub" and "jti" claims by @cleder in #1088
• Development: Add pyupgrade as a pre-commit hook by @kurtmckee in #1109
• Add minimum key length validation for HMAC and RSA keys (CWE-326). Warns by default via InsecureKeyLengthWarning when keys are below minimum recommended lengths per RFC 7518 Section 3.2 (HMAC) and NIST SP 800-131A (RSA). Pass enforce_minimum_key_length=True in options to PyJWT or PyJWS to raise InvalidKeyError instead.
• Refactor PyJWT to own an internal PyJWS instance instead of calling global api_jws functions.

This update for python-PyJWT fixes the following issues:

• CVE-2026-32597: Fixed unknown crit header extensions accepts (bsc#1259616).

This update for python-PyJWT fixes the following issues:

• CVE-2026-32597: Fixed unknown crit header extensions accepts (bsc#1259616).

This update for python-PyJWT fixes the following issues:

• CVE-2026-32597: Fixed unknown crit header extensions accepts (bsc#1259616).

This update for python-PyJWT fixes the following issue:

Update to PyJWT 2.12.1:

• CVE-2026-32597: PyJWT accepts unknown crit header extensions (bsc#1259616).

Changelog:

Update to 2.12.1:

• Add missing typing_extensions dependency for Python < 3.11 in #1150

Update to 2.12.0:

• Annotate PyJWKSet.keys for pyright by @tamird in #1134
• Close HTTPError response to prevent ResourceWarning on Python 3.14 by @veeceey in #1133
• Do not keep algorithms dict in PyJWK instances by @akx in #1143
• Use PyJWK algorithm when encoding without explicit algorithm in #1148
• Docs: Add PyJWKClient API reference and document the two-tier caching system (JWK Set cache and signing key LRU cache).

Update to 2.11.0:

• Enforce ECDSA curve validation per RFC 7518 Section 3.4.
• Fix build system warnings by @kurtmckee in #1105
• Validate key against allowed types for Algorithm family in #964
• Add iterator for JWKSet in #1041
• Validate iss claim is a string during encoding and decoding by @pachewise in #1040
• Improve typing/logic for options in decode, decode_complete by @pachewise in #1045
• Declare float supported type for lifespan and timeout by @nikitagashkov in #1068
• Fix SyntaxWarnings/DeprecationWarnings caused by invalid escape sequences by @kurtmckee in #1103
• Development: Build a shared wheel once to speed up test suite setup times by @kurtmckee in #1114
• Development: Test type annotations across all supported Python versions, increase the strictness of the type checking, and remove the mypy pre-commit hook by @kurtmckee in #1112
• Support Python 3.14, and test against PyPy 3.10 and 3.11 by @kurtmckee in #1104
• Development: Migrate to build to test package building in CI by @kurtmckee in #1108
• Development: Improve coverage config and eliminate unused test suite code by @kurtmckee in #1115
• Docs: Standardize CHANGELOG links to PRs by @kurtmckee in #1110
• Docs: Fix Read the Docs builds by @kurtmckee in #1111
• Docs: Add example of using leeway with nbf by @djw8605 in #1034
• Docs: Refactored docs with autodoc; added PyJWS and jwt.algorithms docs by @pachewise in #1045
• Docs: Documentation improvements for "sub" and "jti" claims by @cleder in #1088
• Development: Add pyupgrade as a pre-commit hook by @kurtmckee in #1109
• Add minimum key length validation for HMAC and RSA keys (CWE-326). Warns by default via InsecureKeyLengthWarning when keys are below minimum recommended lengths per RFC 7518 Section 3.2 (HMAC) and NIST SP 800-131A (RSA). Pass enforce_minimum_key_length=True in options to PyJWT or PyJWS to raise InvalidKeyError instead.
• Refactor PyJWT to own an internal PyJWS instance instead of calling global api_jws functions.

This update for python-PyJWT fixes the following issue:

• CVE-2026-32597: validate the crit Header Parameter defined in RFC 7515 (bsc#1259616).

This update for python-PyJWT fixes the following issues:

Update to PyJWT 2.12.1:

• CVE-2024-53861: prevent partial matching of the Issuer field (bsc#1234038).
• CVE-2026-32597: validate the crit Header Parameter defined in RFC 7515 (bsc#1259616).

Changelog:

Update to 2.12.1:

• Add missing typing_extensions dependency for Python < 3.11 in #1150

Update to 2.12.0:

• Annotate PyJWKSet.keys for pyright by @tamird in #1134
• Close HTTPError response to prevent ResourceWarning on Python 3.14 by @veeceey in #1133
• Do not keep algorithms dict in PyJWK instances by @akx in #1143
• Use PyJWK algorithm when encoding without explicit algorithm in #1148
• Docs: Add PyJWKClient API reference and document the two-tier caching system (JWK Set cache and signing key LRU cache).

Update to 2.11.0:

• Enforce ECDSA curve validation per RFC 7518 Section 3.4.
• Fix build system warnings by @kurtmckee in #1105
• Validate key against allowed types for Algorithm family in #964
• Add iterator for JWKSet in #1041
• Validate iss claim is a string during encoding and decoding by @pachewise in #1040
• Improve typing/logic for options in decode, decode_complete by @pachewise in #1045
• Declare float supported type for lifespan and timeout by @nikitagashkov in #1068
• Fix SyntaxWarnings/DeprecationWarnings caused by invalid escape sequences by @kurtmckee in #1103
• Development: Build a shared wheel once to speed up test suite setup times by @kurtmckee in #1114
• Development: Test type annotations across all supported Python versions, increase the strictness of the type checking, and remove the mypy pre-commit hook by @kurtmckee in #1112
• Support Python 3.14, and test against PyPy 3.10 and 3.11 by @kurtmckee in #1104
• Development: Migrate to build to test package building in CI by @kurtmckee in #1108
• Development: Improve coverage config and eliminate unused test suite code by @kurtmckee in #1115
• Docs: Standardize CHANGELOG links to PRs by @kurtmckee in #1110
• Docs: Fix Read the Docs builds by @kurtmckee in #1111
• Docs: Add example of using leeway with nbf by @djw8605 in #1034
• Docs: Refactored docs with autodoc; added PyJWS and jwt.algorithms docs by @pachewise in #1045
• Docs: Documentation improvements for "sub" and "jti" claims by @cleder in #1088
• Development: Add pyupgrade as a pre-commit hook by @kurtmckee in #1109
• Add minimum key length validation for HMAC and RSA keys (CWE-326). Warns by default via InsecureKeyLengthWarning when keys are below minimum recommended lengths per RFC 7518 Section 3.2 (HMAC) and NIST SP 800-131A (RSA). Pass enforce_minimum_key_length=True in options to PyJWT or PyJWS to raise InvalidKeyError instead.
• Refactor PyJWT to own an internal PyJWS instance instead of calling global api_jws functions.

Update to 2.10.0:

• chore: use sequence for typing rather than list
• Add support for Python 3.13
• [pre-commit.ci] pre-commit autoupdate
• Add an RTD config file to resolve RTD build failures
• docs: Update iat exception docs
• Remove algorithm requirement for JWT API
• Create SECURITY.md
• docs fix: decode_complete scope and algorithms
• fix doctest for docs/usage.rst
• fix test_utils.py not to xfail
• Correct jwt.decode audience param doc expression
• Add PS256 encoding and decoding usage
• Add API docs for PyJWK
• Refactor project configuration files from setup.cfg to pyproject.toml PEP-518
• Add JWK support to JWT encode
• Update pre-commit hooks to lint pyproject.toml
• Add EdDSA algorithm encoding/decoding usage
• Ruff linter and formatter changes
• Validate sub and jti claims for the token
• Add ES256 usage
• Encode EC keys with a fixed bit length
• Drop support for Python 3.8
• Prepare 2.10.0 release
• Bump codecov/codecov-action from 4 to 5

This update for python-PyJWT fixes the following issue:

Update to PyJWT 2.12.1:

• CVE-2026-32597: PyJWT accepts unknown crit header extensions (bsc#1259616).

Changelog:

Update to 2.12.1:

• Add missing typing_extensions dependency for Python < 3.11 in #1150

Update to 2.12.0:

• Annotate PyJWKSet.keys for pyright by @tamird in #1134
• Close HTTPError response to prevent ResourceWarning on Python 3.14 by @veeceey in #1133
• Do not keep algorithms dict in PyJWK instances by @akx in #1143
• Use PyJWK algorithm when encoding without explicit algorithm in #1148
• Docs: Add PyJWKClient API reference and document the two-tier caching system (JWK Set cache and signing key LRU cache).

Update to 2.11.0:

• Enforce ECDSA curve validation per RFC 7518 Section 3.4.
• Fix build system warnings by @kurtmckee in #1105
• Validate key against allowed types for Algorithm family in #964
• Add iterator for JWKSet in #1041
• Validate iss claim is a string during encoding and decoding by @pachewise in #1040
• Improve typing/logic for options in decode, decode_complete by @pachewise in #1045
• Declare float supported type for lifespan and timeout by @nikitagashkov in #1068
• Fix SyntaxWarnings/DeprecationWarnings caused by invalid escape sequences by @kurtmckee in #1103
• Development: Build a shared wheel once to speed up test suite setup times by @kurtmckee in #1114
• Development: Test type annotations across all supported Python versions, increase the strictness of the type checking, and remove the mypy pre-commit hook by @kurtmckee in #1112
• Support Python 3.14, and test against PyPy 3.10 and 3.11 by @kurtmckee in #1104
• Development: Migrate to build to test package building in CI by @kurtmckee in #1108
• Development: Improve coverage config and eliminate unused test suite code by @kurtmckee in #1115
• Docs: Standardize CHANGELOG links to PRs by @kurtmckee in #1110
• Docs: Fix Read the Docs builds by @kurtmckee in #1111
• Docs: Add example of using leeway with nbf by @djw8605 in #1034
• Docs: Refactored docs with autodoc; added PyJWS and jwt.algorithms docs by @pachewise in #1045
• Docs: Documentation improvements for "sub" and "jti" claims by @cleder in #1088
• Development: Add pyupgrade as a pre-commit hook by @kurtmckee in #1109
• Add minimum key length validation for HMAC and RSA keys (CWE-326). Warns by default via InsecureKeyLengthWarning when keys are below minimum recommended lengths per RFC 7518 Section 3.2 (HMAC) and NIST SP 800-131A (RSA). Pass enforce_minimum_key_length=True in options to PyJWT or PyJWS to raise InvalidKeyError instead.
• Refactor PyJWT to own an internal PyJWS instance instead of calling global api_jws functions.

It was discovered that PyJWT did not validate the critical header parameter, contrary to the RFC specification expectations. A remote attacker could possibly use this issue to bypass certain authentication checks and restrictions.