CriticalCVE-2026-53266

    Linux Kernel Out-of-Bounds Write Vulnerability (CVE-2026-53266)

    Published Last modified In CISA KEV since Sources: pwn.watch, SUSE, Red Hat, Debian LTS, Ubuntu, CVE.org, Msrc Update Guide, BSI

    What is affected, what to do

    A flaw was found in the Linux kernel's netfilter bridge ebtables SNAT (Source Network Address Translation) module. This vulnerability allows a local attacker on a system configured with specific bridge netfilter rules to improperly modify underlying memory pages during an ARP (Address Resolution Protocol) sender hardware address rewrite.

    The vulnerability is being actively exploited; treat it as a priority. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Conflicting version data — version display is hidden until the data is resolved.

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    8.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    8.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: pwn.watch, SUSE, Red Hat, Debian LTS, Ubuntu, CVE.org, Msrc Update Guide, BSI

    0.9 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 60.8

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    192.94 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    8.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    8.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.9 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    60.8
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 18 September 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-787

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The bug needs no authentication but does require a foothold on the same L2 segment, high attack complexity and a specific ebtables SNAT configuration with ARP rewrite. Once triggered, the impact is serious: writes into page-cache-backed file pages can tamper with file contents and crash the kernel, hitting both integrity and availability hard. CISA has not flagged ransomware use, and exploitation likelihood is currently moderate. Likely targets are virtualisation, container and edge-gateway hosts running software bridges. If such hosts sit in KRITIS or production networks, treat this as high priority and patch within days; hosts that never load ebt_snat can follow the regular patch cycle.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Patch the kernel: Update to the fixed stable releases: 5.10.259, 5.15.210, 6.1.176, 6.6.143 or 6.12.94. The upstream fix is titled "netfilter: bridge: make ebt_snat ARP rewrite writable". For distribution kernels (RHEL, SUSE, Debian, Ubuntu, Proxmox), a patch is available from the vendor — look up the exact package version in the vendor advisory. Reboot afterwards and confirm with uname -r.
      • Scope exposure: Only the ebtables SNAT target with ARP rewrite reaches the vulnerable path. Run lsmod | grep -E 'ebt_snat|ebtable_nat' and check ebtables -t nat -L --Lc (or nft list ruleset) for rules using --snat-arp. Prioritise hypervisors, container hosts, software-bridge appliances, Linux routers and OT/IoT gateways.
      • Remove the ARP rewrite: If you cannot patch immediately, strip --snat-arp from every SNAT rule. If bridge SNAT isn't required at all, delete the rule entirely.
      • Block the module: On hosts with no need for it, prevent ebt_snat from loading: echo "install ebt_snat /bin/false" > /etc/modprobe.d/cve-2026-53266.conf. If it is already loaded but unused, unload it with modprobe -r ebt_snat.
      • Flag EoL kernels: Unmaintained branches (e.g. 5.4.x, 5.8.x, 5.9.x) will not receive a fix. Isolate these hosts and raise an emergency change to migrate them to a supported LTS branch.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation (L2): The attack vector is adjacent-network. Place bridge hosts in dedicated VLANs and enable port security, DHCP snooping and Dynamic ARP Inspection on access switches, so crafted ARP frames are dropped before they reach the host.
      • Namespace hardening: Stop unprivileged users from building their own bridge and ebtables setup inside a user namespace. Set sysctl -w user.max_user_namespaces=0 where rootless containers aren't used. On Debian/Ubuntu, use kernel.unprivileged_userns_clone=0 or kernel.apparmor_restrict_unprivileged_userns=1 instead.
      • Least privilege: Drop CAP_NET_ADMIN from containers and pods, for example with Kubernetes securityContext.capabilities.drop: ["ALL"] and the PodSecurity "restricted" profile. Use a seccomp profile that blocks unshare and clone with CLONE_NEWUSER.
      • Integrity controls: The flaw writes into page-cache pages of imported files. Enable IMA/EVM or dm-verity on system partitions, and run AIDE or package verification (rpm -Va, debsums -c) on a schedule.
      • Configuration management: Add a compliance check (Ansible, Puppet or a CIS benchmark extension) that alerts when ebt_snat is loaded or --snat-arp appears in persisted ebtables configuration.

    3. Runbook step 3

      Detection rules

      • auditd – bridge firewall changes: Monitor type=NETFILTER_CFG events with family=7 (NFPROTO_BRIDGE) and table=nat. Example SPL: index=linux sourcetype=linux_audit type=NETFILTER_CFG family=7 table=nat | stats count by host, auid, comm. Alert when the actor isn't your config-management tooling.
      • auditd – module loads: Add the rule -a always,exit -F arch=b64 -S init_module,finit_module -k modload and alert on ebt_snat or ebtable_nat loading outside maintenance windows.
      • Namespace abuse: Use Sysmon for Linux (EID 1) or your EDR to watch for unshare -Urn, ip link add ... type bridge or ebtables -t nat -A ... --snat-arp run by non-root users or container processes. Sigma shape: process.command_line|contains|all: ['ebtables', 'snat-arp'].
      • Kernel log: Hunt journald/syslog for BUG:, KASAN: slab-out-of-bounds, general protection fault or oopses with skb_store_bits or ebt_snat_tg in the call trace.
      • Network telemetry: In Zeek arp.log, look for unusual sender MAC/IP flips and ARP bursts from a single segment. Suricata ARP decode-event rules can supplement this. Correlate these events in time with AIDE or IMA mismatches on binaries.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A flaw was found in the Linux kernel's netfilter bridge ebtables SNAT (Source Network Address Translation) module. This vulnerability allows a local attacker on a system configured with specific bridge netfilter rules to improperly modify underlying memory pages during an ARP (Address Resolution Protocol) sender hardware address rewrite. This could lead to unintended system behavior, a denial of service, or potentially local privilege escalation, where an attacker gains higher access rights than intended.

    Source: pwn.watch, suse_csaf, redhat_csaf, Debian LTS Advisories, Ubuntu Security Notices, cvelistv5, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE), Microsoft Security Update Guide, BSI WID Portal, BSI CSAF

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    LinuxLinux
    • 6.7 – < 6.12.94
    • 6.13 – < 6.18.36
    • 5.4.73 – < 5.5
    • 5.11 – < 5.15.210
    • 5.9.2 – < 5.10
    • —
    • 5.8.17 – < 5.9
    • 5.16 – < 6.1.176
    • 5.10 – < 5.10.259
    • 6.19 – < 7.0.13
    • 6.2 – < 6.6.143
    • 6.12.94
    • 6.18.36
    • 5.5
    • 5.15.210
    • 5.10
    • 7.1
    • 5.9
    • 6.1.176
    • 5.10.259
    • 7.0.13
    • 6.6.143
    IBMDataPower Gateway
    • < 11.0.0.3
    • < 10.6.0.11
    • < 10.5.0.23
    • 11.0.0.3
    • 10.6.0.11
    • 10.5.0.23
    IBMQRadar SIEM
    • <7.5.0 UP15 IF06
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxbullseye
    Linuxdebianlinux-6.1bullseye
    Linuxubuntulinux-oracle-7.0noble
    Linuxlinuxlinux_kernel7.1
    Linuxlinuxlinux_kernel—

    Weakness classes (CWE)

    • CWE-787Out-of-bounds Write

      Base

      The product writes data past the end, or before the beginning, of the intended buffer.

      Entry at MITRE CWE-787

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    PoC-in-GitHub (nomi-sec)CVE-2026-53266 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentchanged
      {"id":"CVE-2026-53266","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-18T14:40:13.592810Z"}
      {"id":"CVE-2026-53266","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-18T00:00:00+00:00"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. NVD analysis modifiedNVD

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Reference typeadded
      —
      CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-53266 Types: US Government Resource

      Source identifier: nvd@nist.gov

    3. CISA KEV entry updated9119a7d8…

      4 individual changes: Date Added, Due Date, Required Action, Vulnerability Name

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Date Addedadded
      —
      2026-09-18
      Due Dateadded
      —
      2026-09-18
      Required Actionadded
      —
      2026-09-18
      Vulnerability Nameadded
      —
      2026-09-18

      Source identifier: 9119a7d8-5eab-497f-8521-727c672e3725

    4. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-53266
      SSVC assessmentchanged
      {"id":"CVE-2026-53266","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-18T13:17:28.192271Z"}
      {"id":"CVE-2026-53266","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-18T14:40:13.592810Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    5. Record modifiedLinux

      Show 24 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/153ea96c806aea395daba907a4f88480b6ad5093
      Referenceadded
      —
      https://git.kernel.org/stable/c/67ba971ae02514d85818fe0c32549ab4bfa3bf49
      Referenceadded
      —
      https://git.kernel.org/stable/c/76280b78cc9f23bdc6438e10ad6dff148ef8375b
      Referenceadded
      —
      https://git.kernel.org/stable/c/afd64b59c3de9bbbdd3759e834fdc55cda716e0b
      Referenceadded
      —
      https://git.kernel.org/stable/c/b18675263db1147c8e1cab625400c13a0d87bd2d
      Referenceadded
      —
      https://git.kernel.org/stable/c/b7e91939ba9be805a62a257fa4e227dffbb88fa0
      Referenceadded
      —
      https://git.kernel.org/stable/c/bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87
      Referenceadded
      —
      https://git.kernel.org/stable/c/c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5
      Referenceremoved
      https://git.kernel.org/stable/c/153ea96c806aea395daba907a4f88480b6ad5093
      —
      Referenceremoved
      https://git.kernel.org/stable/c/67ba971ae02514d85818fe0c32549ab4bfa3bf49
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      Referenceremoved
      https://git.kernel.org/stable/c/76280b78cc9f23bdc6438e10ad6dff148ef8375b
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      Referenceremoved
      https://git.kernel.org/stable/c/afd64b59c3de9bbbdd3759e834fdc55cda716e0b
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      https://git.kernel.org/stable/c/b18675263db1147c8e1cab625400c13a0d87bd2d
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      Referenceremoved
      https://git.kernel.org/stable/c/b7e91939ba9be805a62a257fa4e227dffbb88fa0
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      https://git.kernel.org/stable/c/bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87
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      Referenceremoved
      https://git.kernel.org/stable/c/c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/153ea96c806aea395daba907a4f88480b6ad5093 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/67ba971ae02514d85818fe0c32549ab4bfa3bf49 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/76280b78cc9f23bdc6438e10ad6dff148ef8375b Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/afd64b59c3de9bbbdd3759e834fdc55cda716e0b Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/b18675263db1147c8e1cab625400c13a0d87bd2d Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/b7e91939ba9be805a62a257fa4e227dffbb88fa0 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5 Types: Patch
      —

      Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    Show 2 older changes

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Weakness type: CWE-787

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      CWE-787
      SSVC assessmentadded
      —
      {"id":"CVE-2026-53266","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-18T13:17:28.192271Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Initial analysis by NVDNVD

      Newly listed as affected:
      • Linux Kernel (5.8.17 – before 5.9; 5.16 – before 6.1.176; 6.2 – before 6.6.143; 5.11 – before 5.15.210; 6.13 – before 6.18.36; 6.7 – before 6.12.94; 6.19 – before 7.0.13; 5.4.73 – before 5.5; 5.9.2 – before 5.10.259; 6 individual versions)
      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      NVD-CWE-noinfo
      Product configurationadded
      —
      OR *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.8.17 up to (excluding) 5.9 *cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.16 up to (excluding) 6.1.176 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.2 up to (excluding) 6.6.143 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.11 up to (excluding) 5.15.210 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.13 up to (excluding) 6.18.36 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.7 up to (excluding) 6.12.94 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.19 up to (excluding) 7.0.13 *cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc6:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.4.73 up to (excluding) 5.5 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.9.2 up to (excluding) 5.10.259
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/153ea96c806aea395daba907a4f88480b6ad5093 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/67ba971ae02514d85818fe0c32549ab4bfa3bf49 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/76280b78cc9f23bdc6438e10ad6dff148ef8375b Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/afd64b59c3de9bbbdd3759e834fdc55cda716e0b Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/b18675263db1147c8e1cab625400c13a0d87bd2d Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/b7e91939ba9be805a62a257fa4e227dffbb88fa0 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5 Types: Patch

      Source identifier: nvd@nist.gov

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