What is CVE-2026-53266?

CVE-2026-53266 is netfilter: bridge: make ebt_snat ARP rewrite writable. The supplied enrichment data classifies it as Memory Corruption mapped to CWE-787 Out-of-bounds Write.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Yes: CISA KEV signal present. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

Is there a public exploit?

3 public PoC repositories reported; 1 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with Not reported where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-53266 using CVSS 8.8, EPSS 1%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Treat as emergency remediation because CISA KEV status is present. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

CISA KEVhighMemory Corruptionpublic exploit

CVE-2026-53266

CVE-2026-53266 — netfilter: bridge: make ebt_snat ARP rewrite writable

Q: Is it in CISA KEV?

Yes. The supplied enrichment data lists CVE-2026-53266 in CISA KEV with 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.. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

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().

Published Jun 25, 2026Updated Sep 18, 2026Sources: NVD, Linux (CNA), CISA, FIRST EPSS, GitHub, Microsoft MSRC, Red Hat (VEX), SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Confirmed

CISA KEV, listed Sep 18, 2026

EPSS

ahead of 49% of scored CVEs

Affects

Linux

25 products listed

CVSS base

8.8

high · 3 sources

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

Active

none · proof-of-concept · active

Automatable

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

Upgrade Linux to a fixed release (0 to < 5.10). Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

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.

Federal deadline Sep 21, 2026 — passed 15 days ago

Red Hat VEX · CVE-2026-53266

fixed453affected99not affected42

vendor_fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 The system must be rebooted for …

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Treat as emergency remediation because CISA KEV status is present.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741	Vulnerable
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741 to < 76280b78cc9f23bdc6438e10ad6dff148ef8375b	Vulnerable
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741	Vulnerable
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741	Vulnerable
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741 to < 153ea96c806aea395daba907a4f88480b6ad5093	Vulnerable
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741	Vulnerable
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741	Vulnerable
Linux	Linux	63137bc5882a1882c553d389fdeeeace86ee1741 to < 67ba971ae02514d85818fe0c32549ab4bfa3bf49	Vulnerable
Linux	Linux	2f3839075a5f8dcf116c1abe35b36b018ac62445	Vulnerable
Linux	Linux	51ba2945a8ef65ae437c8f9ba05f0343aa82ae5b	Vulnerable
Linux	Linux	b7d23c2c87584eb429f115c078ed511be8b18e29	Vulnerable
Linux	Linux	5.4.73 to < 5.5	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Availability

High

Confidentiality

High

Integrity

High

Scope

Changed

Attack Complexity

Low

Attack Vector

Local

Privileges Req

Low

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
8.8	CVSS 3.1	high	2	6	CNA, Linux (CNA)
6.8	CVSS 3.1	medium	—	—	Microsoft
7.5	CVSS 3.1	high	—	—	Red Hat (VEX)

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

Weakness & attack patterns

CWE-787Out-of-bounds Write

Inferred from the weakness class — not observed against this CVE.

CAPEC-100 · Overflow BuffersCAPEC-123 · Buffer Manipulation

CISA KEV details

CISA lists a CVE here once it has evidence of exploitation against real targets.

CISAThat month →

Listed

Sep 18, 2026

Federal deadline

Sep 21, 2026

passed 15 days ago

Ransomware use

Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a date to argue against.

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

1 of the 3 sampled are weaponized

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Search application, proxy, and WAF logs for requests touching /eth_hdr().
Monitor for scanner or exploit-pattern traffic after 3 public PoC repositories were reported.

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added to CISA KEV catalog
Sep 18, 2026 · CISA
Added · CVSS 3.1 8.8 (AV:L)
Sep 18, 2026 · NVD
Initial · CVE published
Jun 25, 2026 · NVD

Source activity

Readings a source repeats on a schedule, counted rather than listed.

4×ModifiedJun 25, 2026 – Sep 18, 2026 · SOCRadar CTI
1×1 time mentioned on 1 Telegram channelJun 28, 2026 · SOCRadar CTI

References

20 on the record

git.kernel.org/stable/c/153ea96c806aea395daba907a4f88480b6ad5093
Patch, NIST, Vendor Advisory
git.kernel.org/stable/c/67ba971ae02514d85818fe0c32549ab4bfa3bf49
Patch, NIST, Vendor Advisory
git.kernel.org/stable/c/76280b78cc9f23bdc6438e10ad6dff148ef8375b
Patch, NIST, Vendor Advisory
git.kernel.org/stable/c/afd64b59c3de9bbbdd3759e834fdc55cda716e0b
Patch, NIST, Vendor Advisory
git.kernel.org/stable/c/b18675263db1147c8e1cab625400c13a0d87bd2d
Patch, NIST, Vendor Advisory
git.kernel.org/stable/c/b7e91939ba9be805a62a257fa4e227dffbb88fa0
Patch, NIST, Vendor Advisory
git.kernel.org/stable/c/bf84ad7c7a9ede46e31afaa41a1ba06a159e8c87
Patch, NIST, Vendor Advisory
git.kernel.org/stable/c/c9b5ff59feffb92a147a84a5aa28acd2cb8ff4c5
Patch, NIST, Vendor Advisory

Coverage

3 stories from the feeds we poll

Elsewhere on this site

Linuxevery CVE for this vendor
Microsoftevery CVE for this vendor
September 2026what else CISA listed
Memory Corruptionsame class
CWE-787other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-53266 is netfilter: bridge: make ebt_snat ARP rewrite writable, a high vulnerability affecting Linux, azl3 kernel 6.6.141.1-1 on Azure Linux 3.0 from Linux, Microsoft. The current evidence lists it in CISA KEV, and the exploit status is: Yes: CISA KEV signal present. Public exploit evidence is: 3 public PoC repositories reported; 1 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 8.8 describes technical severity, while EPSS 1% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.