PHP Memory Corruption Vulnerability (CVE-2026-109618)

Catalog analysis: CISA added this entry on October 26, 2026. The entry reflects catalog information retrieved on October 27, 2026, not a snapshot archived on the inclusion date. This site’s publication date is shown separately. Check current vendor guidance before acting.

What the vulnerability is

CVE-2026-109618 is an out-of-memory corruption vulnerability affecting the PHP language. This flaw allows an unauthenticated attacker to achieve remote code execution (RCE) on the target system. The vulnerability is associated with several memory-related weaknesses, including CWE-416 (Use After Free), CWE-755 (Out-of-bounds Write), and CWE-824 (Out-of-bounds Write), among others.

Exposure and applicability

This vulnerability affects systems running the PHP product. Because PHP is an open-source component used across a vast array of web servers, third-party libraries, and proprietary implementations, exposure is widespread. The risk is highest for assets with direct internet exposure where unauthenticated requests can reach the PHP interpreter.

Remediation priorities

Our analysis suggests prioritizing remediation based on asset criticality and network visibility. Organizations should take the following steps:

1. Identify Affected Assets: Inventory all servers and cloud environments utilizing PHP to determine which versions are deployed.
2. Apply Vendor Mitigations: Implement updates or mitigations as specified in the official PHP Group instructions.
3. Prioritize Internet-Facing Systems: In alignment with risk-based prioritization (such as BOD 26-04), assets exposed to the public internet should be patched first to reduce the likelihood of unauthenticated RCE.
4. Perform Forensic Triage: Because this vulnerability is listed in CISA’s Known Exploited Vulnerabilities catalog and requires forensic triage, defenders should inspect affected systems for signs of compromise prior to or during the patching process.

How to validate remediation

Verification must go beyond confirming a version number. To ensure exposure has been reduced, we recommend:

• Configuration Audit: Confirm that the updated PHP binary is actively loaded and running in the production environment across all nodes.
• Deployment Verification: Use configuration management tools to verify that mitigations are applied consistently across the fleet, rather than on a per-server basis.
• Exposure Testing: Validate that internet-facing entry points are restricted or that the patched version of PHP is handling requests without triggering memory corruption errors.

Limits and open questions

Applying a patch reduces the likelihood of exploitation but does not guarantee total immunity from similar memory corruption flaws. There remains uncertainty regarding whether this vulnerability has been utilized in specific ransomware campaigns, as current data lists this status as unknown. Additionally, because PHP is often embedded in other products, organizations may be dependent on third-party vendors to release updates for their specific implementations of the language.

Source and editorial note

CVE-2026-109618: PHP Memory Corruption Vulnerability · Source date: October 26, 2026 · Retrieved October 27, 2026.

Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.

Request a Vulnerability Assessment