On October 21, 2026, the PHP project announced security releases for two critical vulnerabilities in PHP. CVE-2026-109618 can corrupt memory during out-of-memory (OOM) handling, while CVE-2026-109619 is a use-after-free flaw involving state retained between requests. Both have a CVSSv4 score of 9.2 and both can allow for unauthenticated remote code execution (RCE) with the web worker's privileges.
CVE
CVSSv4
Description
RCE via OOM corruption
RCE via stale global state
All installations serving web requests are at risk, including PHP-FPM, Apache mod_php, php-cgi, FrankenPHP, and LiteSpeed. The vendor considers mod_php the highest risk because exploitation can succeed before any application code runs.
The advisories report that a successful RCE exploit was developed during research, including achieving RCE against Apache mod_php and PHP-FPM through different attack paths. As of October 21, 2026, there are multiple indications that this research is being independently reproduced, and a viable exploit is expected to be made public soon.
Due to the extremely high deployment of PHP based web applications, exploitation in-the-wild is expected. Rapid7 recommends updating affected installations on an emergency basis, outside of normal patch cycles.
Technical overviewCVE-2026-109618: Memory corruption during OOM handling
According to the OOM advisory, PHP can abruptly abandon request processing when a memory allocation fails. If internal request data is only partly initialized, that exit can leave invalid data for request cleanup to use. Crafted multipart requests, used for forms and file uploads, can exhaust memory even when their size appears to meet PHP's configured limits. Application operations that allocate memory in response to attacker input can also trigger OOM.
Apache mod_php runs cleanup even when request startup fails, enabling the demonstrated attack before application code executes. The advisory reports RCE over HTTP with default PHP input and memory limits, including multi-worker prefork deployments. PHP-FPM terminates a worker when startup fails, preventing that particular sequence. Source analysis supports FPM susceptibility after successful startup, but the advisory reports no complete FPM exploit for this CVE. Exploit portability and reliability depend on the PHP build, extensions, frontend behavior, and memory layout.
CVE-2026-109619: Use after free across requests
PHP can reuse a worker process to handle multiple HTTP requests. The stale-state advisory describes internal state that still points to memory freed at the end of an earlier request. A later request handled by the same worker can access that stale value before normal initialization clears it. Fatal errors, including memory exhaustion and execution timeouts, can interrupt state cleanup; some nonfatal diagnostics during shutdown can also repopulate error state after it was reset.
The advisory confirms RCE against mod_php through PHP 8.5's fatal error backtrace feature, when fatal_error_backtraces is enabled (the default), where a later initialization diagnostic accesses stale backtrace state. It also confirms session lifecycle RCE against mod_php and FPM. Session upload progress, PHP's upload-tracking feature, is enabled by default and can act as an early consumer of stale session or decoder state before normal initialization; reaching this consumer does not itself require an application call to session_start().
The validated FPM session path requires a suitable application operation to leave state behind after successful startup, followed by a fatal error and another request that consumes the stale state through session upload progress. Both requests must reach the same worker. Multiple workers and worker recycling can reduce success per request, but do not eliminate the condition.
Mitigation guidance
PHP has released fixes for both vulnerabilities. Organizations should prioritize updating to the appropriate fixed release or a vendor package containing both complete patches. The PHP advisories list these affected and fixed versions:
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PHP 8.2 releases before 8.2.35: Update to 8.2.35
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PHP 8.3 releases before 8.3.36: Update to 8.3.36
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PHP 8.4 releases before 8.4.27: Update to 8.4.27
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PHP 8.5 releases before 8.5.12: Update to 8.5.12
Linux distributions and long-term support vendors received patches in advance; check your vendor for updated packages. PHP 8.1 and older no longer receive routine upstream updates. For this incident, PHP has supplied limited source backports for PHP 7.4, 8.0, and 8.1. Organizations running older branches should obtain a vendor fix, use the source backports described in the PHP announcement, or upgrade to a supported version. PHP also warns that rpms.remirepo.net will not have updates on October 21, 2026, and urges its users to switch to distribution packages or build from source.
Note that an update containing both complete fixes is the only complete remediation.
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CVE-2026-109618 and CVE-2026-109619: Critical Unauthenticated Remote Code Execution in PHP