ssl::select_next_proto use after free

In `openssl` versions before `0.10.70`, `ssl::select_next_proto` can return a slice pointing into the `server` argument's buffer but with a lifetime bound to the `client` argument. In situations where the `server` buffer's lifetime is shorter than the `client` buffer's, this can cause a use after free. This could cause the server to crash or to return arbitrary memory contents to the client. `openssl` 0.10.70 fixes the signature of `ssl::select_next_proto` to properly constrain the output buffer's lifetime to that of both input buffers. In standard usage of `ssl::select_next_proto` in the callback passed to `SslContextBuilder::set_alpn_select_callback`, code is only affected if the `server` buffer is constructed *within* the callback. For example: Not vulnerable - the server buffer has a `'static` lifetime: ```rust builder.set_alpn_select_callback(|_, client_protos| { ssl::select_next_proto(b"\x02h2", client_protos).ok_or_else(AlpnError::NOACK) }); ``` Not vulnerable - the server buffer outlives the handshake: ```rust let server_protos = b"\x02h2".to_vec(); builder.set_alpn_select_callback(|_, client_protos| { ssl::select_next_proto(&server_protos, client_protos).ok_or_else(AlpnError::NOACK) }); ``` Vulnerable - the server buffer is freed when the callback returns: ```rust builder.set_alpn_select_callback(|_, client_protos| { let server_protos = b"\x02h2".to_vec(); ssl::select_next_proto(&server_protos, client_protos).ok_or_else(AlpnError::NOACK) }); ```

Source published

2 Feb 2025 12:00:00 UTC

Source modified

12 Oct 2026 18:00:12 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

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