CVE-2026-53266 — Kernel
HIGHCVE-2026-53266 is a high-severity (CVSS 8.8) Out-of-bounds Write vulnerability in Kernel. It is in CISA's Known Exploited Vulnerabilities catalog (added 2026-09-18) — treat it as actively exploited and patch now. A fix is available for Kernel — see the affected versions and patch details below.
netfilter: bridge: make ebt_snat ARP rewrite writable
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2026-09-18. Federal agencies were required to remediate by 2026-09-21.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2026-53266.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-53266 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
KernelReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.
Description
In the Linux kernel, the following vulnerability has been resolved:
netfilter: bridge: make ebt_snat ARP rewrite writable
The ebtables SNAT target keeps the Ethernet source address rewrite behind skb_ensure_writable(skb, 0). This is intentional: at the bridge ebtables hooks the Ethernet header is addressed through skb_mac_header()/eth_hdr(), while skb->data points at the Ethernet payload. Asking skb_ensure_writable() for ETH_HLEN bytes would check the payload, not the Ethernet header, and would reintroduce the small packet regression fixed by commit 63137bc5882a.
However, the optional ARP sender hardware address rewrite is different. It writes through skb_store_bits() at an offset relative to skb->data:
skb_store_bits(skb, sizeof(struct arphdr), info->mac, ETH_ALEN)
skb_header_pointer() only safely reads the ARP header; it does not make the later sender hardware address range writable. If that range is still held in a nonlinear skb fragment backed by a splice-imported file page, skb_store_bits() maps the frag page and copies the new MAC address directly into it.
Ensure the ARP SHA range is writable before reading the ARP header and before calling skb_store_bits().
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 5.10.0&&< 5.10.259 | 5.10.259 |
Affected Products
linux kernellinuxDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Kernel to 5.10.259 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53266 is resolved across your whole dependency graph.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
An Important flaw in the Linux kernel's ebtables SNAT target allows a local attacker to achieve privilege escalation, memory corruption, or denial of service. This vulnerability requires specific bridge netfilter rules to be configured, limiting its impact to systems with such specialized network configurations.
Disable ARP hardware address rewriting in ebtables SNAT rules, or remove ebtables SNAT rules that operate on ARP traffic on bridge interfaces.Source: Red Hat security advisory for CVE-2026-53266 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| NVIDIA for RHEL 10 | kernel-0:6.12.0-231.20.el10nv | RHSA-2026:72059 |
| Red Hat Enterprise Linux 10 | kernel-0:6.12.0-211.59.1.el10_2 | RHSA-2026:71233 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | kernel-0:6.12.0-55.106.1.el10_0 | RHSA-2026:71326 |
| Red Hat Enterprise Linux 6 Extended Lifecycle Support - EXTENSION | kernel-0:2.6.32-754.64.1.el6 | RHSA-2026:73732 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | kernel-rt-0:3.10.0-1160.164.1.rt56.1316.el7 | RHSA-2026:71657 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | kernel-0:3.10.0-1160.164.1.el7 | RHSA-2026:71687 |
| Red Hat Enterprise Linux 8 | kernel-rt-0:4.18.0-553.143.1.rt7.484.el8_10 | RHSA-2026:39082 |
| Red Hat Enterprise Linux 8 | kernel-0:4.18.0-553.143.1.el8_10 | RHSA-2026:39083 |
Frequently Asked Questions
Is CVE-2026-53266 in your dependencies?
Find it across Linux, including transitive dependencies.