René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Add SSRF protection for HTTP client redirects","articleBody":"## Summary\n\nThe SDK creates `httpx.AsyncClient` with `follow_redirects=True` but no redirect validation. A malicious MCP server can redirect requests to internal network addresses (`http://localhost`, `http://169.254.169.254`, `http://metadata.google.internal`), enabling SSRF attacks.\n\n## Location\n\n`src/mcp/shared/_httpx_utils.py` — the shared httpx client factory.\n\n## Proposed Fix\n\n1. **Default:** Block HTTPS-to-HTTP downgrades on redirects\n2. Provide configurable `RedirectPolicy` presets:\n   - `BLOCK_SCHEME_DOWNGRADE` (default) — block HTTPS→HTTP redirects\n   - `ENFORCE_HTTPS` (strict) — only allow HTTPS destinations\n   - `ALLOW_ALL` (legacy) — current behavior, no restrictions\n3. Consider also blocking redirects to private/link-local IP ranges\n","author":{"url":"https://github.com/maxisbey","@type":"Person","name":"maxisbey"},"datePublished":"2026-02-19T20:25:06.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/2106/python-sdk/issues/2106"}