CVE-2026-82416

## Summary In worker mode under concurrency, FrankenPHP can hand a PHP session id from one request to another when PHP's `session` extension is loaded as a shared module instead of being statically linked into the FrankenPHP binary. A request presenting `Cookie: session=A` can have `session_id()` resolve to `B` (a different concurrent client's id) or to a stale id from a previous request served by the same worker thread. ## Impact - **Security:** cross-user session exposure / session hijacking in worker mode. Same impact class as CVE-2026-24894. - **Functional:** users are intermittently logged out; their cookie's session is ignored and they receive a foreign or empty session. ## Affected / not affected Exposure is determined by how the `session` extension is linked in the PHP build FrankenPHP is compiled against, **not** by the FrankenPHP release: - **Affected:** any build where the `session` extension is not visible to FrankenPHP at compile time, i.e. loaded as a shared / out-of-tree module (`extension=session` in an ini). This includes the RPM and Debian packages and other packaged `php-zts` distributions that ship `session` as a shared extension under `conf.d`. - **Not affected:** builds where `session` is statically compiled into the PHP that FrankenPHP links against, such as the official static binaries and Docker images. There, the reset code below is compiled in and clears the id every request. The C session-reset code is unchanged across 1.11.x-1.12.x, so this is not a code regression between releases. A "1.12.2 works / 1.12.3 leaks" observation on the same host reflects two differently-built packages, not a source change. The persistent-zval helpers (#2366) are compiled only under `FRANKENPHP_TEST` and are unrelated. ## Root cause FrankenPHP resets per-request session state in `frankenphp_reset_session_state()`, which releases `PS(id)` so the next `session_start()` re-reads the request cookie. That whole function is guarded by `#ifdef HAVE_PHP_SESSION