vLLM Anthropic API and speech-to-text heap address information leak

CVE-2026-54236 is an information disclosure vulnerability in vLLM caused by an incomplete fix for CVE-2026-22778. Prior to vLLM 0.23.1rc0, several error-handling paths return raw exception text to clients by embedding str(exc) directly in responses instead of passing the message through the sanitize_message helper intended to strip object-representation memory addresses. The affected paths include the Anthropic API router in vllm/entrypoints/anthropic/api_router.py for POST /v1/messages and POST /v1/messages/count_tokens, the Server-Sent Events streaming converter in vllm/entrypoints/anthropic/serving.py, and the realtime speech-to-text WebSocket handler in vllm/entrypoints/speech_to_text/realtime/connection.py. These handlers catch exceptions locally and construct JSONResponse objects themselves, bypassing the sanitizing global FastAPI exception handler; WebSocket frames also do not traverse that handler chain. An unauthenticated attacker can trigger the issue by supplying malformed image bytes through Anthropic Messages API image content parts, causing PIL.Image.open to raise UnidentifiedImageError. The resulting exception string can include a Python object representation such as a BytesIO repr with a literal heap address, which is then reflected to the client in the error response.