CVE-2026-53266: Linux Kernel

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

Yes, if you run Linux Kernel. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-09-18, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-21; treat that as the outer limit, not the target.
EPSS 0.8%, percentile 57: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 57% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
Editorial verdict: Patch this week. Linux Kernel: Five Exploited Root Bugs Added to CISA KEV — Five local root bugs, all with fixes and most with public exploits, are now confirmed exploited; get every Linux host onto a current kernel and reboot this week, container hosts, CI runners and shared servers first.

What it is

In the Linux kernel, the following vulnerability has been resolved: netfilter: bridge: make ebtsnat ARP rewrite writable The ebtables SNAT target keeps the Ethernet source address rewrite behind skbensurewritable(skb, 0). This is intentional: at the bridge ebtables hooks the Ethernet header is addressed through skbmacheader()/ethhdr(), while skb->data points at the Ethernet payload. Asking skbensurewritable() for ETHHLEN 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 skbstorebits() at an offset relative to skb->data: skbstorebits(skb, sizeof(struct arphdr), info->mac, ETHALEN) skbheaderpointer() 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, skbstorebits() 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 skbstorebits().

CISA’s summary

Linux Kernel contains an out-of-bounds write vulnerability in the ebtables SNAT target which allows an ARP sender hardware address rewrite to write directly into a nonlinear socket-buffer fragment backed by a splice-imported file page. The impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

Weakness type: CWE-787.

Product: Linux Kernel · Assigned by: Linux · Published: 2026-06-25

Affected and fixed versions

Vendor	Product	Affected versions (per CVE record)
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741 < bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87, 63137bc5882a1882c553d389fdeeeace86ee1741 < 76280b78cc9f23bdc6438e10ad6dff148ef8375b, 63137bc5882a1882c553d389fdeeeace86ee1741 < b7e91939ba9be805a62a257fa4e227dffbb88fa0, 63137bc5882a1882c553d389fdeeeace86ee1741 <…
Linux	Linux	5.10

Severity scores

Scored by	CVSS	Score	Vector
Linux	3.1	8.8 High	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`

Attack vector: local access needed
Attack complexity: low
Privileges required: low (any account)
User interaction: none
Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

CISA KEV: added 2026-09-18; federal due date 2026-09-21. Known ransomware use: Unknown.
CISA required action: 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.
CISA SSVC assessment: exploitation active, automatable no, technical impact total.
FIRST EPSS (model of 2026-10-21): 0.83% probability of exploitation activity in the next 30 days; percentile 57.

Timeline

2026-06-25 — CVE record published by Linux
2026-09-18 — Added to CISA’s Known Exploited Vulnerabilities catalog
2026-09-18 — erroneo.us brief: Linux Kernel: Five Exploited Root Bugs Added to CISA KEV
2026-09-19 — CVE record last updated
2026-09-21 — CISA remediation deadline for US federal agencies

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.