rust-openssl ssl::select_next_proto use after free

### Impact `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. ### Patches `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. ### Workarounds 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) }); ``` ### References https://github.com/sfackler/rust-openssl/pull/2360

Source published

3 Feb 2025 17:56:46 UTC

Source modified

10 Sep 2026 03:50:06 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N

Publisher rating · MODERATE