PHP Discloses CVE-2026-115560 Session Deserialization Flaw
The PHP Foundation recently published a security disclosure detailing a remote code execution risk. Specifically, maintainers registered the issue as CVE-2026-115560 across national vulnerability databases. However, developers opted against deploying an immediate emergency point release. The flaw demands a peculiar alignment of configuration settings and runtime execution paths. Consequently, the team considers the practical threat profile comparatively modest.
Strict Configuration Requirements for Exploitation
According to preliminary technical findings, exploitation succeeds only under an intricate sequence of operational factors. Specifically, an application must initially configure session.serialize_handler to php_binary or php_serialize. Subsequently, the script must alter this setting to php at runtime via ini_set(). Furthermore, the application must invoke session_start() immediately following that modification. Crucially, the target server must also keep session.upload_progress.enabled active throughout processing.
The session.serialize_handler directive governs the internal format that PHP uses to store session state. In an official PHP security announcement, developers clarified that applications avoiding runtime handler manipulation remain secure. Therefore, services can safely preserve upload tracking capabilities without introducing compromise vectors. Maintainers assess this dynamic handler reconfiguration as extraordinarily rare across modern production codebases.
Recommended Mitigation and Deployment Strategy
Importantly, this newly cataloged risk remains entirely distinct from the earlier PHP2Shell vulnerability. Because reproduction requires specialized operational conditions, maintainers issued an interim mitigation rather than an unverified emergency patch. Upstream engineers will include formal code remedies within upcoming standard release cycles.
Immediate Server Workarounds
Meanwhile, the PHP Foundation advises affected organizations to disable file upload progress tracking immediately. Specifically, administrators should assign session.upload_progress.enabled to zero within server configuration profiles. Furthermore, teams should preserve this directive until official distribution updates become accessible. Fortunately, hosting environments that already deactivated this feature require zero administrative intervention.
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