RUSTSEC-2025-0004: ssl::select_next_proto use after free

| Details | |
| --- | --- |
| Package | `openssl` |
| Version | `0.10.68` |
| URL | https://github.com/sfackler/rust-openssl/security/advisories/GHSA-rpmj-rpgj-qmpm |
| Patched Versions | >=0.10.70 |
| Aliases | [CVE-2025-24898](https://nvd.nist.gov/vuln/detail/CVE-2025-24898), [GHSA-rpmj-rpgj-qmpm](https://github.com/advisories/GHSA-rpmj-rpgj-qmpm) |

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)
});
```