CVE-2026-46300: Linux Kernel Missing Initialization of a Variable Vulnerability

What happened

Linux Kernel contains a missing initialization of a variable vulnerability that could allow for unintended modification of page-cache-backed data via failure to preserve the shared-fragment marker during socket buffer coalescing, causing ESP input processing to decrypt shared fragments in place. This vulnerability can be chained with CVE-2026-109618 and CVE-2026-109619 to implant PHP webshells and run commands as root.

CISA added CVE-2026-46300 to its Known Exploited Vulnerabilities catalog on 2026-10-28, which means there is evidence of real-world attacks.

Who is affected

Organisations running Linux Kernel. Check the vendor advisory in the sources for the exact affected versions.

Why it matters

It has a CVSS score of 7.8. Exploitation is already happening, so exposed systems are at immediate risk.

What to do now

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Find every instance of Kernel in your environment, patch internet-facing systems first, and review logs for signs of compromise.

Sources

• CISA Known Exploited Vulnerabilities catalog
• NVD entry for CVE-2026-46300
• https://git.kernel.org/stable/c/3599e6b3cc1ada96883d496a50a210d3afbb6987
• https://git.kernel.org/stable/c/2f2b16022a2e10ca7bccfb98db5ed2ec0f72641c
• https://git.kernel.org/stable/c/9d3e5fd19fe1063bf607219e8562fbd567b8e8d5
• https://git.kernel.org/stable/c/78bf6b6bb19541d19fbda6242e7cfe2c682763c0
• https://git.kernel.org/stable/c/760e1addc27ba1a7beb4a0a7e8b3e9ec49e7a34e