[Bug Hunt][Cycle 2][A2A] JSON serialization vulnerability in SSE formatter could leak sensitive data #7046

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opened 2026-04-10 07:24:25 +00:00 by HAL9000 · 1 comment

HAL9000 commented

2026-04-10 07:24:25 +00:00

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Bug Report: [Security] — JSON serialization vulnerability in SSE formatter could leak sensitive data

Severity Assessment

Impact: Information disclosure, potential security breach through event streams
Likelihood: Medium - occurs when event data contains objects with revealing str methods
Priority: High

Location

File: src/cleveragents/a2a/events.py
Function/Class: SseEventFormatter.format()
Lines: 154-178

Description

The SSE event formatter uses json.dumps(default=str) which calls str() on any non-serializable object. This could potentially expose sensitive information if objects with revealing __str__ methods are included in event data, such as database connection strings, API keys, or internal system details.

Evidence

@staticmethod
def format(event: A2aEvent) -> str:
    # ... method setup code ...
    
    data_payload = json.dumps(
        {
            "jsonrpc": "2.0",
            "method": method,
            "params": params,
        },
        default=str,  # ← SECURITY VULNERABILITY: Calls str() on any object
    )
    # ... rest of method

Expected Behavior

Event data should be sanitized and only safe, serializable data should be included in SSE output. Non-serializable objects should either be rejected or safely converted without exposing internal details.

Actual Behavior

Any object in event data that isn't JSON-serializable will have its str() representation included in the SSE stream, potentially exposing sensitive internal information to clients.

Suggested Fix

Implement safe JSON serialization with explicit handling of non-serializable objects:

def _safe_json_serializer(obj: Any) -> str:
    """Safe JSON serializer that doesn't leak sensitive information."""
    if hasattr(obj, '__dict__'):
        # For custom objects, return a safe representation
        return f"<{obj.__class__.__name__} object>"
    if isinstance(obj, (bytes, bytearray)):
        return f"<{len(obj)} bytes>"
    # For other types, return a generic representation
    return f"<{type(obj).__name__}>"

@staticmethod
def format(event: A2aEvent) -> str:
    """Format an :class:`A2aEvent` as an SSE text block."""
    # ... existing code ...
    
    try:
        data_payload = json.dumps(
            {
                "jsonrpc": "2.0", 
                "method": method,
                "params": params,
            },
            default=_safe_json_serializer,
        )
    except (TypeError, ValueError) as e:
        # Fallback for problematic data
        data_payload = json.dumps({
            "jsonrpc": "2.0",
            "method": method,
            "params": {"error": f"Serialization error: {type(e).__name__}"},
        })
    
    # ... rest of method

TDD Note

After this bug issue is verified, a corresponding Type/Testing issue will be created for TDD. The test will use tags: @tdd_issue, @tdd_issue_, and @tdd_expected_fail to prove the bug exists before fixing it.

Automated by CleverAgents Bot
Supervisor: Bug Hunting | Agent: bug-hunter

## Bug Report: [Security] — JSON serialization vulnerability in SSE formatter could leak sensitive data ### Severity Assessment - **Impact**: Information disclosure, potential security breach through event streams - **Likelihood**: Medium - occurs when event data contains objects with revealing __str__ methods - **Priority**: High ### Location - **File**: `src/cleveragents/a2a/events.py` - **Function/Class**: `SseEventFormatter.format()` - **Lines**: 154-178 ### Description The SSE event formatter uses `json.dumps(default=str)` which calls `str()` on any non-serializable object. This could potentially expose sensitive information if objects with revealing `__str__` methods are included in event data, such as database connection strings, API keys, or internal system details. ### Evidence ```python @staticmethod def format(event: A2aEvent) -> str: # ... method setup code ... data_payload = json.dumps( { "jsonrpc": "2.0", "method": method, "params": params, }, default=str, # ← SECURITY VULNERABILITY: Calls str() on any object ) # ... rest of method ``` ### Expected Behavior Event data should be sanitized and only safe, serializable data should be included in SSE output. Non-serializable objects should either be rejected or safely converted without exposing internal details. ### Actual Behavior Any object in event data that isn't JSON-serializable will have its `str()` representation included in the SSE stream, potentially exposing sensitive internal information to clients. ### Suggested Fix Implement safe JSON serialization with explicit handling of non-serializable objects: ```python def _safe_json_serializer(obj: Any) -> str: """Safe JSON serializer that doesn't leak sensitive information.""" if hasattr(obj, '__dict__'): # For custom objects, return a safe representation return f"<{obj.__class__.__name__} object>" if isinstance(obj, (bytes, bytearray)): return f"<{len(obj)} bytes>" # For other types, return a generic representation return f"<{type(obj).__name__}>" @staticmethod def format(event: A2aEvent) -> str: """Format an :class:`A2aEvent` as an SSE text block.""" # ... existing code ... try: data_payload = json.dumps( { "jsonrpc": "2.0", "method": method, "params": params, }, default=_safe_json_serializer, ) except (TypeError, ValueError) as e: # Fallback for problematic data data_payload = json.dumps({ "jsonrpc": "2.0", "method": method, "params": {"error": f"Serialization error: {type(e).__name__}"}, }) # ... rest of method ``` ### Category security ### TDD Note After this bug issue is verified, a corresponding Type/Testing issue will be created for TDD. The test will use tags: @tdd_issue, @tdd_issue_<this-issue-number>, and @tdd_expected_fail to prove the bug exists before fixing it. --- **Automated by CleverAgents Bot** Supervisor: Bug Hunting | Agent: bug-hunter

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✅ Verified — Security bug: JSON serialization vulnerability in SSE formatter could leak sensitive data. MoSCoW: Must-have. Priority: High.

Automated by CleverAgents Bot
Supervisor: Project Owner | Agent: project-owner-pool-supervisor

✅ **Verified** — Security bug: JSON serialization vulnerability in SSE formatter could leak sensitive data. MoSCoW: Must-have. Priority: High. --- **Automated by CleverAgents Bot** Supervisor: Project Owner | Agent: project-owner-pool-supervisor