FrankenPHP: Cross-request PHP session ID leak in worker mode when the session extension is a shared module

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

FrankenPHP is a modern application server for PHP. Prior to 1.12.5, FrankenPHP worker mode can retain PHP session state between requests when the session extension is loaded as a shared module and is unavailable through HAVE_PHP_SESSION at compile time. In this build configuration, frankenphp_reset_session_state() is compiled out, PS(id) can survive a request boundary, and a subsequent session_start() can ignore the new request's cookie because an identifier is already present. Under concurrent requests, session_id() can therefore return another client's identifier or a stale identifier from a previous request on the same worker thread, causing cross-user session exposure, possible session hijacking, and intermittent logout behavior. Builds with the session extension statically linked, including the official static binaries and Docker images, are not affected. This issue is fixed in version 1.12.5.

Source published

13 Oct 2026 16:20:53 UTC

Source modified

13 Oct 2026 20:22:02 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 7.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L

FrankenPHP is a modern application server for PHP. Prior to 1.12.5, FrankenPHP worker mode can retain PHP session state between requests when the session extension is loaded as a shared module and is unavailable through HAVE_PHP_SESSION at compile time. In this build configuration, frankenphp_reset_session_state() is compiled out, PS(id) can survive a request boundary, and a subsequent session_start() can ignore the new request's cookie because an identifier is already present. Under concurrent requests, session_id() can therefore return another client's identifier or a stale identifier from a previous request on the same worker thread, causing cross-user session exposure, possible session hijacking, and intermittent logout behavior. Builds with the session extension statically linked, including the official static binaries and Docker images, are not affected. This issue is fixed in version 1.12.5.

Source published

Oct 13, 2026, 4:20:53 PM (timezone not stated)

Source modified

Oct 13, 2026, 8:22:02 PM (timezone not stated)

Observed here

7 Nov 2026 14:32:08 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 7.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L

FrankenPHP is a modern application server for PHP. Prior to 1.12.5, FrankenPHP worker mode can retain PHP session state between requests when the session extension is loaded as a shared module and is unavailable through HAVE_PHP_SESSION at compile time. In this build configuration, frankenphp_reset_session_state() is compiled out, PS(id) can survive a request boundary, and a subsequent session_start() can ignore the new request's cookie because an identifier is already present. Under concurrent requests, session_id() can therefore return another client's identifier or a stale identifier from a previous request on the same worker thread, causing cross-user session exposure, possible session hijacking, and intermittent logout behavior. Builds with the session extension statically linked, including the official static binaries and Docker images, are not affected. This issue is fixed in version 1.12.5.

Source published

13 Oct 2026 17:17:47 UTC

Source modified

16 Oct 2026 20:04:29 UTC

Observed here

25 Oct 2026 16:19:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 7.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L

## 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`, a macro defined only when the session extension headers are present at FrankenPHP compile time (session statically enabled in the PHP build). When `session` is a shared module, `HAVE_PHP_SESSION` is undefined, the reset is compiled out, and `PS(id)` survives the request boundary. PHP's `session_start()` reads the request cookie only when `PS(id)` is `NULL` (`ext/session/session.c`, `try_find_session_id_in_cookies()`: `if (!PS(use_cookies) || PS(id)) return;`). With a stale `PS(id)`, the cookie is ignored and the worker reuses the previous request's id, exposing it to whichever client is served next. ## Reproduction Minimal worker script (`index.php`): ```php <?php $handler = static function () { session_start(); $sent = $_COOKIE['session'] ?? '(none)'; $id = session_id(); header('Content-Type: text/plain'); echo ($sent === '(none)' || $sent === $id) ? "OK sent=$sent id=$id\n" : "LEAK sent=$sent id=$id\n"; session_write_close(); }; while (\frankenphp_handle_request($handler)) {} ``` Run under worker mode with `num 2` (≥2 workers), `session.use_strict_mode=1`, on a PHP build where `session` is a shared module. Pre-create two valid sessions `A` and `B`, then fire concurrent requests alternating the two cookies: ```sh seq 600 | xargs -P32 -I{} sh -c ' c=$([ $(( {} % 2 )) -eq 0 ] && echo A || echo B); curl -s -H "Cookie: session=$c" http://127.0.0.1:8080/' | grep -c LEAK ``` On an affected build a large fraction of responses are `LEAK` (`session_id()` differs from the cookie sent, and `A` and `B` sometimes resolve to the same id). On a statically-linked build the count is always `0`. ## Fix When `HAVE_PHP_SESSION` is undefined, FrankenPHP now resets the `session` module through the module registry on every worker request (its `RSHUTDOWN` releases `PS(id)`, `RINIT` re-initialises the globals), so the per-request cleanup always runs regardless of how the extension is linked. Statically-linked builds are unchanged and keep using `frankenphp_reset_session_state()`. Verified on PHP 8.6-dev ZTS, 2 workers, `session.use_strict_mode=1`, 600 alternating-cookie concurrent requests: before the fix 519/600 leaked; after the fix 0/600. Statically-linked builds stayed at 0/600. ## Workarounds - Use a FrankenPHP build with `session` statically compiled (official static binaries or Docker images). - Or, in the worker loop, after `session_write_close()` call `session_id('')` so the next `session_start()` re-reads the request cookie (with `session.use_strict_mode=1`).

Source published

15 Oct 2026 20:14:29 UTC

Source modified

19 Oct 2026 21:41:08 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L

Publisher rating · HIGH

FrankenPHP: Cross-request PHP session ID leak in worker mode when the session extension is a shared module in github.com/dunglas/frankenphp

Source published

19 Oct 2026 21:08:35 UTC

Source modified

19 Oct 2026 21:31:38 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

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 · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.