Vulnerability report

Trusted Third Party Report Confirmed Confidence In CISA KEV

CVE-2026-53266

netfilter: bridge: make ebt_snat ARP rewrite writable

Linux · affected before bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87

Watch CVE-2026-53266 Browse KEV feed
Severity
CVSS 8.8 · High
Confidence
Confirmed
Exploit status
Trusted Third Party Report
EPSS
0.9%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-53266 is netfilter: bridge: make ebt_snat ARP rewrite writable affecting Linux.

Have exploitation attempts been observed?

Yes. Exploitation attempts have been reported for this vulnerability. Previdian lists it as a known exploited vulnerability. Listed in CISA KEV. Also reported by third-party sources. Confidence is confirmed.

Who is affected?

Linux, including affected before bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87, affected before 76280b78cc9f23bdc6438e10ad6dff148ef8375b, and affected before b7e91939ba9be805a62a257fa4e227dffbb88fa0.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

netfilter: bridge: make ebt_snat ARP rewrite writable

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().

Linux Affected
Linux
Before bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87 Before 76280b78cc9f23bdc6438e10ad6dff148ef8375b Before b7e91939ba9be805a62a257fa4e227dffbb88fa0 Before afd64b59c3de9bbbdd3759e834fdc55cda716e0b Before 153ea96c806aea395daba907a4f88480b6ad5093 Before b18675263db1147c8e1cab625400c13a0d87bd2d Before c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5 Before 67ba971ae02514d85818fe0c32549ab4bfa3bf49 2f3839075a5f8dcf116c1abe35b36b018ac62445 51ba2945a8ef65ae437c8f9ba05f0343aa82ae5b b7d23c2c87584eb429f115c078ed511be8b18e29 Before 5.5 Before 5.9 Before 5.10 5.10
Linux Unaffected
Linux
Before 5.10 Through 5.10.* Through 5.15.* Through 6.1.* Through 6.6.* Through 6.12.* Through 6.18.* Through 7.0.* Through *
Published
25 Jun 2026
Exploitation Attempts Reported
18 Sep 2026
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None

Tags

linux cisa

CVE References

Exploitation evidence

Evidence of exploitation attempts

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploitation Attempts Observed in the Wild

CISA

Recorded 18 Sep 2026

A trusted third party reported exploitation attempts.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CISA First 2026-09-18 14:30 UTC
CVE 2026-09-18 14:50 UTC
The Hacker News 2026-09-19 00:00 UTC
BleepingComputer 2026-09-21 20:12 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

No detection artifacts or sensor request patterns are available for this CVE yet.

Check back as sensor telemetry and scanner integrations are updated.

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

8.8 High

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

0.9%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Out-of-bounds Write CWE-787

Recent mention · BleepingComputer

CISA alerts of active exploitation of three Linux kernel flaws

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) is warning that hackers are exploiting three Linux kernel vulnerabilities, one of them rated critical. [...]

Read full advisory

All Mentions

Recent mention · BleepingComputer

CISA alerts of active exploitation of three Linux kernel flaws

BleepingComputer · 21 Sep 2026

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) is warning that hackers are exploiting three Linux kernel vulnerabilities, one of them rated critical. [...]

Recent mention · Security Affairs

U.S. CISA adds Linux Kernel flaws to its Known Exploited Vulnerabilities catalog

Security Affairs · 20 Sep 2026

U.S. Cybersecurity and Infrastructure Security Agency (CISA) adds Linux Kernel flaws to its Known Exploited Vulnerabilities catalog. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added [1, 2] the following vulnerabilities to its Known Exploited Vulnerabilities (KEV) catalog: Below are detailed descriptions of the flaws: At the time of this writing, there are currently no details on how the […]

Recent mention · The Hacker News

CISA Flags Three Linux Kernel Vulnerabilities Exploited in the Wild

The Hacker News · 19 Sep 2026

Ravie LakshmananSep 19, 2026Vulnerability / Linux The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Friday added three security flaws impacting the Linux kernel to its Known Exploited Vulnerabilities (KEV) catalog, citing evidence of active exploitation. The vulnerabilities are listed below - CVE-2025-39682 (CVSS score: 9.8) - An improper check for unusual or exceptional conditions vulnerability in the TLS receive path that could allow local authenticated users to trigger memory disclosure or denial-of-service (DoS). CVE-2026-53266 (CVSS score: 8.8) - An out-of-bounds...

Timeline

From disclosure to observed exploitation attempts

  1. 20:12 UTC

    KEV confirmed by BleepingComputer

    Exploitation attempts reported by an external source

  2. 00:00 UTC

    KEV confirmed by The Hacker News

    Exploitation attempts reported by an external source

  3. 14:50 UTC

    KEV confirmed by CVE

    Exploitation attempts reported by an external source

  4. 14:30 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  5. 08:39 UTC

    CVE published

    Vulnerability disclosed publicly

  6. 07:44 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

Start 14-day Pro trial Read API docs
  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-53266

Sample API response 
{
  "cve_id": "CVE-2026-53266",
  "confidence": "Confirmed",
  "cvss_score": 8.8,
  "cvss_estimated": false,
  "epss_score": 0.00934,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}