CISA KEV: Linux Kernel CVE-2026-53266 (CVSS 3.1 8.8 HIGH) - Kernel Out-of-Bounds Write Vulnerability

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().

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KEV

criticalPublished September 26, 2026 at 7:48 PM UTC

Blue Goat Risk Score

Blue Goat Cyber MedTech rubric v1.0 · methodology

7.3

of 10

high

CVSS technical

40% · +3.5

3.1 base 8.8 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Patient safety

35% · +1.8

Delay of care

Exploit maturity

15% · +1.5

On CISA KEV (in-the-wild)

MedTech exposure

10% · +0.5

5/10 network-reachable signals

How we got to 7.3

1
CVSS technical severity (40%)
Industry-standard exploitability + impact score. We prefer CVSS 4.0 and fall back to 3.1 per the FDA's Feb 2026 premarket cybersecurity guidance. Missing CVSS scores get a neutral 4.0 so unknown vulns are not over- or under-rated.
3.1 base 8.8 × 40% = +3.52
2
Patient safety impact (35%)
What happens to a patient if this vuln is exploited on a connected device. Auto-inferred from headline, dek, tags, and device class against a curated MedTech keyword library (pacemaker, infusion pump, EHR, PACS, etc.).
Delay of care → 5 × 35% = +1.75
3
Exploit maturity (15%)
Is anyone actually using this in attacks? KEV listing > weaponized exploit > public PoC > none. KEV alone forces tier=critical regardless of CVSS.
On CISA KEV (in-the-wild) → 10 × 15% = +1.50
4
MedTech exposure (10%)
How likely this affects clinical operations: presence in our MedTech feed (+4 baseline), network-reachable signals (+3), known device-class tags (+2), identified MedTech vendor (+1).
Exposure 5/10 × 10% = +0.50

Tier cutoffs: Critical ≥ 8.5 · High 7.0–8.4 · Notable 4.0–6.9 · Info < 4.0. Full methodology, weights, and changelog at /goatfeed/risk-rubric.

Citations

#kev #cve #linux

CISA KEV: Linux Kernel CVE-2026-53266 (CVSS 3.1 8.8 HIGH) - Kernel Out-of-Bounds Write Vulnerability

How we got to 7.3

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