Linux Kernel Variable Initialization Flaw (CVE-2026-46300)

Catalog analysis: CISA added this entry on October 28, 2026. The entry reflects catalog information retrieved on October 29, 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-2026-46300 is a vulnerability in the Linux kernel characterized by the missing initialization of a variable (CWE-456). Specifically, the kernel fails to preserve the shared-fragment marker during socket buffer coalescing. This failure allows for the unintended modification of page-cache-backed data, which causes ESP input processing to decrypt shared fragments in place.

While this flaw is significant on its own, it is particularly critical because it can be chained with CVE-2026-109618 and CVE-2026-109619. This combination of vulnerabilities could allow an attacker to implant PHP webshells and execute commands with root privileges.

Exposure and applicability

This vulnerability affects systems running the Linux kernel that utilize socket buffer coalescing and ESP input processing. Because this is an open-source component, exposure extends across various distributions and proprietary implementations that incorporate the affected kernel code.

Infrastructure owners should prioritize assets that are internet-facing or those where the kernel version has not yet integrated the specific stability patches provided by the upstream project. The risk is highest in environments where the other vulnerabilities in the chain (CVE-2026-109618 and CVE-2026-109619) may also be present.

Remediation priorities

Our analysis suggests that remediation should be prioritized based on the asset’s exposure and its role in the environment. The primary corrective action is to apply the patches provided by the kernel maintainers.

Defenders should focus on:
1. Identifying affected kernels: Cross-referencing current kernel versions against the specific git commits released by kernel.org (e.g., 3599e6b3cc1ada96883d496a50a210d3afbb6987 and associated stable branch updates).
2. Addressing the chain: Since this vulnerability is used in conjunction with CVE-2026-109618 and CVE-2026-109619 to achieve root access, these should be treated as a single high-priority remediation event.
3. Prioritizing internet-facing assets: Systems exposed to external traffic should be patched first to reduce the likelihood of initial entry via this path.

How to validate remediation

Verification must go beyond checking a version number, as different distributions backport fixes differently. To verify that exposure has been reduced, vulnerability management teams should:

• Commit Verification: Verify that the specific fix commits (such as those listed in the kernel.org stable git logs) have been merged into the running kernel image.
• Configuration Audit: Ensure that any compensating controls intended to limit socket buffer manipulation are active while patching is underway.

Confirmation of a successful update is achieved when the binary state of the kernel reflects the logic changes introduced in the official patches, rather than relying solely on a distribution’s release notes.

Limits and open questions

Applying the patch for CVE-2026-46300 addresses the variable initialization flaw but does not inherently resolve the other vulnerabilities (CVE-2026-109618 and CVE-2026-109619) if they are present in the environment. Residual risk remains if any part of the exploit chain remains unpatched.

Additionally, because this is an open-source component used across many different products, there may be a delay between the upstream kernel fix and the availability of patched packages from specific Linux distribution vendors.

Source and editorial note

CVE-2026-46300: Linux Kernel Missing Initialization of a Variable Vulnerability · Source date: October 28, 2026 · Retrieved October 29, 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.

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