CVE-2026-53965

The MCP PHP SDK Composer package mcp/sdk is the official Model Context Protocol SDK for PHP. In versions 0.5.0 through 0.7.0, the HTTP client transport reads a Server-Sent Events response stream incrementally and appends each chunk to an in-memory buffer with no upper bound. The buffer is only...

CVE-2026-53965 MCP PHP SDK: Unbounded SSE buffer in HttpTransport enables client-side denial of service

The MCP PHP SDK Composer package mcp/sdk is the official Model Context Protocol SDK for PHP. In versions 0.5.0 through 0.7.0, the HTTP client transport reads a Server-Sent Events response stream incrementally and appends each chunk to an in-memory buffer with no upper bound. The buffer is only...

CVE-2026-53965 MCP PHP SDK: Unbounded SSE buffer in HttpTransport enables client-side denial of service

The MCP PHP SDK Composer package mcp/sdk is the official Model Context Protocol SDK for PHP. In versions 0.5.0 through 0.7.0, the HTTP client transport reads a Server-Sent Events response stream incrementally and appends each chunk to an in-memory buffer with no upper bound. The buffer is only...

CVE-2026-53965

CVE-2026-53965 affects the MCP PHP SDK (Composer package mcp/sdk), versions 0.5.0 through 0.7.0 . The HttpTransport class's processSSEStream() method appends each 4 KiB read chunk to an in-memory buffer ($this->sseBuffer) with no upper bound ; the buffer is only flushed upon encountering the S...

GHSA-7M52-JW36-44R3 MCP PHP SDK: client HttpTransport SSE buffer (sseBuffer .= chunk) grows unbounded when server withholds the event delimiter

Summary The HTTP client transport in mcp/sdk reads a Server-Sent-Events SSE response stream incrementally and appends each 4 KiB chunk to an in-memory buffer $this-sseBuffer .= $chunk; with no upper bound. The buffer is only ever flushed when an SSE event delimiter "\n\n" appears. A remote MCP...

MCP PHP SDK: client HttpTransport SSE buffer (sseBuffer .= chunk) grows unbounded when server withholds the event delimiter

Summary The HTTP client transport in mcp/sdk reads a Server-Sent-Events SSE response stream incrementally and appends each 4 KiB chunk to an in-memory buffer $this-sseBuffer .= $chunk; with no upper bound. The buffer is only ever flushed when an SSE event delimiter "\n\n" appears. A remote MCP...

Client HttpTransport SSE buffer grows unbounded when server withholds the event delimiter

Summary The HTTP client transport in mcp/sdk reads a Server-Sent-Events SSE response stream incrementally and appends each 4 KiB chunk to an in-memory buffer $this-sseBuffer .= $chunk; with no upper bound. The buffer is only ever flushed when an SSE event delimiter "\n\n" appears. A remote MCP...