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ERROR_PORT_MESSAGE_TOO_LONG
The LPC or ALPC message is too large
ERROR_PORT_MESSAGE_TOO_LONG means a message submitted to a native port request or request/reply operation exceeds the maximum accepted size. The limit can include headers and alignment, not just application payload bytes.
Common causes
- Serializing an unbounded object directly into one IPC message.
- Ignoring protocol header and alignment overhead.
- A length field uses characters while the transport expects bytes.
- Client and server disagree about structure version.
Diagnosis
Log total message size, payload size, header version, and negotiated maximum. Validate all nested lengths and protect additions from overflow. Reproduce with the exact architecture and OS build.
Resolution
Split data into bounded chunks, place bulk data in shared memory or a file-backed section, and send only descriptors through the port. Define explicit protocol limits before allocation.
Security guidance
Reject oversized inbound messages early. Do not allocate based solely on an untrusted declared length, and do not truncate structured messages because truncation can change their meaning.
References
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