Answer in brief
CVE-2026-53965 records a High severity vulnerability in MCP PHP SDK: Unbounded SSE buffer in HttpTransport enables client-side denial of service. The current sources do not mark it as known exploited. The current feed maps mcp/sdk (composer), modelcontextprotocol/php-sdk (generic), mcp/sdk (packagist). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps mcp/sdk (composer), modelcontextprotocol/php-sdk (generic), mcp/sdk (packagist). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| mcp/sdkcomposer | >=0.5.0,<0.7.1 | 0.7.1 |
| modelcontextprotocol/php-sdkgeneric | >= 0.5.0, < 0.7.1 | Not reported |
| mcp/sdkpackagist | >=0.5.0 <0.7.1 | 0.7.1 |
Published upstream
Aug 25, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 25, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 19, 2026
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 flushed when an SSE event delimiter, a double newline, is found, so a remote MCP server that streams response bytes without ever sending the delimiter causes the buffer to grow without limit. A malicious, compromised, or man-in-the-middle-controlled server that the client connects to over the HTTP transport can exploit this to exhaust the client process's memory, triggering a fatal allocation error or OS out-of-memory kill and denying service to the MCP client. The issue affects any client using HttpTransport against an untrusted server endpoint and does not require authentication or user interaction beyond initiating the connection. This issue is fixed in version 0.7.1.
Quoted source text, attributed separately from HOL analysis.