CVE-2026-122233 in FrankenPHP
Summary
by MITRE • 11/04/2026
FrankenPHP before 1.13.4 contains an information disclosure vulnerability in worker mode that fails to clear last HTTP stream response headers between requests, because the reset only happens in RSHUTDOWN, which worker requests skip. Later requests calling http_get_last_response_headers() can read headers fetched by earlier requests on the same worker thread, exposing other users' Set-Cookie or token headers from backend APIs.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in FrankenPHP versions prior to 1.13.4 represents a critical information disclosure flaw inherent to its long-running worker mode architecture. In standard PHP execution models, each request is typically isolated within its own process or thread lifecycle, ensuring that state from one request does not leak into another. However, FrankenPHP utilizes persistent workers to improve performance by reusing the same PHP instance across multiple HTTP requests. The core technical flaw lies in the handling of HTTP response headers during this reuse cycle. Specifically, the framework fails to clear the last HTTP stream response headers between successive requests served by the same worker thread. This cleanup operation is currently gated exclusively within the RSHUTDOWN phase, which corresponds to the end-of-request lifecycle hook that processes long-running workers effectively skip or bypass in their continuous execution loop. Consequently, the internal state variables holding header data remain populated with information from previous interactions rather than being reset to a neutral state for new incoming requests.
This architectural oversight leads directly to a severe cross-user data leakage scenario. When an attacker initiates a request that triggers the retrieval of last response headers via functions such as http_get_last_response_headers(), they are not receiving headers associated with their own transaction, but rather those from a prior request handled by the same worker process. Since web servers often distribute requests to available workers in a round-robin or least-connections fashion, an attacker can strategically time their requests to target specific worker threads that have recently served other users. By doing so, they can extract sensitive headers such as Set-Cookie values containing session identifiers, authentication tokens, or CSRF protections intended for legitimate users of the backend API. This effectively allows unauthorized access to user sessions and potentially facilitates account takeover attacks if these credentials are subsequently used by the attacker.
From a classification perspective, this vulnerability aligns with CWE-209: Generation of Error Message Containing Sensitive Information, although it is more accurately described as CWE-200: Exposure of Sensitive Information to an Unauthorized Actor under the broader category of information leakage. In terms of offensive security frameworks, this flaw maps directly to ATT&CK technique T1530: Data from Local System, specifically involving data staging and exfiltration through application-level state manipulation rather than direct file system access. The attack vector is remote and requires no authentication for the initial probe, making it particularly dangerous in public-facing environments where worker distribution logic can be manipulated to increase the probability of hitting a target thread with stale sensitive headers.
The operational impact extends beyond simple session hijacking. If the leaked headers contain security-related tokens or configuration details from backend APIs, attackers may gain insights into internal network structures, API endpoints, or authentication mechanisms that should remain opaque. This exposure undermines the confidentiality guarantees expected in web applications and violates fundamental principles of request isolation. For organizations relying on FrankenPHP for high-performance PHP deployments, this vulnerability necessitates immediate attention as it compromises user privacy and security posture without requiring complex exploitation chains beyond simple HTTP requests.
Mitigation strategies must focus on ensuring strict state reset between worker iterations. The primary remediation is to upgrade to version 1.13.4 or later of FrankenPHP, where the developers have addressed this lifecycle management issue by ensuring headers are cleared appropriately within the request handling flow rather than relying solely on shutdown hooks that workers bypass. In environments where upgrading is not immediately feasible, temporary workarounds might include configuring the web server to limit worker reuse frequency or implementing application-level middleware that explicitly clears global header variables at the start of each script execution, although such code changes are less reliable and performance-intensive compared to a framework patch. Additionally, monitoring for unusual patterns in cookie access or token usage can help detect exploitation attempts while mitigation measures are deployed.