CVE-2026-54275

Summary

The server_hostname TLS SNI check can be bypassed when an existing connection is reused.

Impact

If an application makes multiple requests to the same domain, but with different per-request server_hostname parameters, then the later calls may succeed by reusing the existing connection when they should have been rejected due to the TLS SNI check.

Workaround

Disable keep_alive if you need to change the server_hostname check between requests.

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Patch: https://github.com/aio-libs/aiohttp/commit/0ca2b6c28a25726527a8b60f25960262a91ed0e0