---
title: "CVE-2026-53266: Linux Kernel Out-of-Bounds Write Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-53266/
description: "CVE-2026-53266 (Linux Kernel): Exploited in the wild (CISA KEV). In the Linux kernel, the following vulnerability has been resolved: netfilter: bridge: make…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-06-25
date_modified: 2026-10-21
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-53266"
kev: true
cvss: 8.8
epss: 0.00827
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-53266: Linux Kernel Out-of-Bounds Write Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- 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().

## Affected products (CVE record)

- Linux Linux: 63137bc5882a1882c553d389fdeeeace86ee1741 < bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87, 63137bc5882a1882c553d389fdeeeace86ee1741 < 76280b78cc9f23bdc6438e10ad6dff148ef8375b, 63137bc5882a1882c553d389fdeeeace86ee1741 < b7e91939ba9be805a62a257fa4e227dffbb88fa0, 63137bc5882a1882c553d389fdeeeace86ee1741 < afd64b59c3de9bbbdd3759e834fdc55cda716e0b, 63137bc5882a1882c553d389fdeeeace86ee1741 < 153ea96c806aea395daba907a4f88480b6ad5093, 63137bc5882a1882c553d389fdeeeace86ee1741 < b18675263db1147c8e1cab625400c13a0d87bd2d, 63137bc5882a1882c553d389fdeeeace86ee1741 < c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5, 63137bc5882a1882c553d389fdeeeace86ee1741 < 67ba971ae02514d85818fe0c32549ab4bfa3bf49, 2f3839075a5f8dcf116c1abe35b36b018ac62445, 51ba2945a8ef65ae437c8f9ba05f0343aa82ae5b, b7d23c2c87584eb429f115c078ed511be8b18e29, 5.4.73 < 5.5
- Linux Linux: 5.10

## Severity

- Linux CVSS 3.1: 8.8 `CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`

## Exploitation

- 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.

## Sources

- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/76280b78cc9f23bdc6438e10ad6dff148ef8375b)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/b7e91939ba9be805a62a257fa4e227dffbb88fa0)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/afd64b59c3de9bbbdd3759e834fdc55cda716e0b)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/153ea96c806aea395daba907a4f88480b6ad5093)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/b18675263db1147c8e1cab625400c13a0d87bd2d)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/stable/c/67ba971ae02514d85818fe0c32549ab4bfa3bf49)
- [CVE.org record CVE-2026-53266](https://www.cve.org/CVERecord?id=CVE-2026-53266)
- [NVD entry CVE-2026-53266](https://nvd.nist.gov/vuln/detail/CVE-2026-53266)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-53266)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk)

---
Source page: https://erroneo.us/security/cve/CVE-2026-53266/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt