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Actively exploited

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

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.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 28 Oct 2026.
  • Rated High severity (CVSS 7.8, scored by Vendor).
The Vulnerability

What It Is

In the Linux kernel, the following vulnerability has been resolved: net: skbuff: preserve shared-frag marker during coalescing skb_try_coalesce() can attach paged frags from @from to @to. If @from has SKBFL_SHARED_FRAG set, the resulting @to skb can contain the same externally-owned or page-cache-backed frags, but the shared-frag marker is currently lost. That breaks the invariant relied on by later in-place writers. In particular, ESP input checks skb_has_shared_frag() before deciding whether an uncloned nonlinear skb can skip skb_cow_data(). If TCP receive coalescing has moved shared frags into an unmarked skb, ESP can see skb_has_shared_frag() as false and decrypt in place over page-cache backed frags. Propagate SKBFL_SHARED_FRAG when skb_try_coalesce() transfers paged frags. The tailroom copy path does not need the marker because it copies bytes into @to's linear data rather than transferring frag descriptors.

Affected Versions

ProductVersions
Linux Linuxcef401de7be8c4e155c6746bfccf721a4fa5fab9 to before 3599e6b3cc1ada96883d496a50a210d3afbb6987
cef401de7be8c4e155c6746bfccf721a4fa5fab9 to before 2f2b16022a2e10ca7bccfb98db5ed2ec0f72641c
cef401de7be8c4e155c6746bfccf721a4fa5fab9 to before 9d3e5fd19fe1063bf607219e8562fbd567b8e8d5
cef401de7be8c4e155c6746bfccf721a4fa5fab9 to before 78bf6b6bb19541d19fbda6242e7cfe2c682763c0
cef401de7be8c4e155c6746bfccf721a4fa5fab9 to before 760e1addc27ba1a7beb4a0a7e8b3e9ec49e7a34e
cef401de7be8c4e155c6746bfccf721a4fa5fab9 to before 3bd9e113d50034db99d7ef69fd8e5242d15e414a
Linux Linux3.9

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Linux Kernel. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    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.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated high, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 31 Oct 2026 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

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All 32 exploited Linux vulnerabilities

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2026-46300
  3. CVE record: CVE-2026-46300
  4. FIRST EPSS
  5. git.kernel.org/stable/c/3599e6b3cc1ada96883d496a50a210d3afbb6987
  6. git.kernel.org/stable/c/2f2b16022a2e10ca7bccfb98db5ed2ec0f72641c
  7. git.kernel.org/stable/c/9d3e5fd19fe1063bf607219e8562fbd567b8e8d5
  8. git.kernel.org/stable/c/78bf6b6bb19541d19fbda6242e7cfe2c682763c0
  9. git.kernel.org/stable/c/760e1addc27ba1a7beb4a0a7e8b3e9ec49e7a34e
  10. git.kernel.org/stable/c/3bd9e113d50034db99d7ef69fd8e5242d15e414a
  11. git.kernel.org/stable/c/3884358a9286b17f389a72b1426fc4547c23c111
  12. git.kernel.org/stable/c/f84eca5817390257cef78013d0112481c503b4a3