CVE-2026-53965: MCP PHP SDK: client HttpTransport SSE buffer (sseBuffer .= chunk) grows unbounded when server withholds the event delimiter

high Affects mcp/sdk. Feed 2026.10.29.4, updated 2026-10-29; published 2026-08-19.

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

Package: mcp/sdk Composer
Affected versions: >=0.5.0 and <0.7.1
Fixed in: 0.7.1
Severity: high
Exploitation: not on CISA KEV · EPSS 1% (49.4th percentile)
Published: 2026-08-19
Source: osv.dev

References

Am I affected?

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