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Fix potential DoS issue with p2c header #336

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Dec 26, 2023
Merged

Fix potential DoS issue with p2c header #336

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5 changes: 5 additions & 0 deletions jwcrypto/jwa.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,8 @@

# Implements RFC 7518 - JSON Web Algorithms (JWA)

default_max_pbkdf2_iterations = 16384


class JWAAlgorithm(metaclass=ABCMeta):

Expand Down Expand Up @@ -588,6 +590,9 @@ def __init__(self):
self.aeskwmap = {128: _A128KW, 192: _A192KW, 256: _A256KW}

def _get_key(self, alg, key, p2s, p2c):
if p2c > default_max_pbkdf2_iterations:
raise ValueError('Invalid p2c value, too large')

if not isinstance(key, JWK):
# backwards compatibility for old interface
if isinstance(key, bytes):
Expand Down
12 changes: 12 additions & 0 deletions jwcrypto/tests.py
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Expand Up @@ -2099,6 +2099,18 @@ def test_pbes2_hs256_aeskw_custom_params(self):
key = jwk.JWK.from_password('password')
self.assertRaises(ValueError, enc.add_recipient, key)

# Test p2c iteration checks
maxiter = jwa.default_max_pbkdf2_iterations
p2cenc = jwe.JWE(plaintext='plain',
protected={"alg": "PBES2-HS256+A128KW",
"enc": "A256CBC-HS512",
"p2c": maxiter + 1,
"p2s": base64url_encode("A" * 16)})
with self.assertRaisesRegex(ValueError, 'too large'):
p2cenc.add_recipient(key)
jwa.default_max_pbkdf2_iterations += 2
p2cenc.add_recipient(key)


class JWATests(unittest.TestCase):
def test_jwa_create(self):
Expand Down