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fix: skip malformed agent card signature headers #1335

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fix: skip malformed agent card signature headers #1335

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8 changes: 8 additions & 0 deletions src/a2a/utils/signing.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import binascii
import json

from collections.abc import Callable
Expand Down Expand Up @@ -144,6 +145,13 @@ def signature_verifier(
agent_card_signature.protected.encode('utf-8')
).decode('utf-8')
protected_header = json.loads(protected_header_json)
except (binascii.Error, UnicodeDecodeError, json.JSONDecodeError):
continue

if not isinstance(protected_header, dict):
continue

try:
kid = protected_header.get('kid')
jku = protected_header.get('jku')
verification_key = key_provider(kid, jku)
Expand Down
26 changes: 26 additions & 0 deletions tests/utils/test_signing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -143,6 +143,32 @@ def test_signer_and_verifier_symmetric_multiple_signatures(
verifier_wrong_key(signed_card)


def test_verifier_skips_malformed_protected_header(

@Iwaniukooo11 Iwaniukooo11 Oct 14, 2026

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Please extend the test to also cover json.JSONDecodeError, UnicodeDecodeError, and the not isinstance(protected_header, dict) guard

sample_agent_card: AgentCard,
):
key = 'key12345'
signer = signing.create_agent_card_signer(
signing_key=key,
protected_header={'alg': 'HS384', 'kid': 'key1', 'jku': None},
)
verifier = signing.create_signature_verifier(
create_key_provider(key), ['HS256', 'HS384', 'ES256', 'RS256']
)
malformed = AgentCardSignature(
protected='!!!not-base64url!!!', signature='invalid'
)

invalid_card = AgentCard()
invalid_card.CopyFrom(sample_agent_card)
invalid_card.signatures.append(malformed)
with pytest.raises(signing.InvalidSignaturesError):
verifier(invalid_card)

valid_card = signer(sample_agent_card)
valid_card.signatures.insert(0, malformed)
verifier(valid_card)


def test_signer_and_verifier_asymmetric(sample_agent_card: AgentCard):
"""Test the agent card signing and verification process with an asymmetric key encryption."""
private_key = ec.generate_private_key(ec.SECP256R1())
Expand Down
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