CVE-2026-24894

EUVD-2026-6698 · Published Feb 12, 2026

FrankenPHP leaks session data between requests in worker mode

Summary

When running FrankenPHP in worker mode, the $_SESSION superglobal is not correctly reset between requests. This allows a subsequent request processed by the same worker to access the $_SESSION data of the previous request (potentially belonging to a different user) before session_start() is called.

Details

In standard PHP execution, the environment is torn down completely after every request. In FrankenPHP's worker mode, the application stays in memory, and superglobals are manually reset between requests.

The vulnerability exists because $_SESSION is stored in the Zend Engine's symbol table (EG(symbol_table)). While the standard PHP request shutdown (RSHUTDOWN) decrements the reference count of the session data, it does not remove the $_SESSION variable itself from the symbol table. FrankenPHP's reset logic (frankenphp_reset_super_globals) previously cleared other superglobals but failed to explicitly delete $_SESSION.

Consequently, until session_start() is called in the new request (which re-initializes the variable), the $_SESSION array retains the data from the previous request processed by that specific worker thread.

Impact

This is a cross-request data leakage vulnerability.

Confidentiality: If an application reads $_SESSION before calling session_start(), it can access sensitive information (authentication tokens, user IDs, PII) belonging to the previous user.
Logic Errors / Impersonation: If application logic relies on $_SESSION being empty or unset to detect a "guest" state, or checks for specific keys in $_SESSION prior to session initialization, a malicious actor (or accidental race condition) could trigger privilege escalation or user impersonation.

This affects only users running FrankenPHP in worker mode and not session_start() for each request, which is done by default by most frameworks.

PoC

The following steps demonstrate the issue (derived from the regression tests added in the fix):

Client A sends a request that starts a session and sets sensitive data:

// Request 1
session_start();
$_SESSION['secret'] = 'AliceData';
session_write_close();

Client B (or the same client without cookies) sends a request to the same worker. This script checks $_SESSION without starting a session:

// Request 2
// session_start() is NOT called
if (!empty($_SESSION)) {
    echo "Leaked Data: " . $_SESSION['secret'];
}

Result: Client B receives "Leaked Data: AliceData".

Workarounds

Ensure session_start() is called immediately at the entry point of your worker script to overwrite any residual data (though this may not cover all edge cases if middleware runs before the controller).
Manually unset $_SESSION at the very beginning of the worker loop, before handling the request.

Technologies

Php FrankenphpDunglas Frankenphp

Weaknesses

CWE-613CWE-384CWE-269

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Initial Access Privilege Escalation

T1190Exploit Public-Facing Application T1548Abuse Elevation Control Mechanism

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.