Executive Summary

CVE-2026-53266 exposes a write‑back vulnerability in the Linux kernel’s ebtables SNAT target. The ARP sender hardware address (SHA) field is written via skb_store_bits() without guaranteeing the underlying skb fragment is writable, allowing an attacker to overwrite the MAC address in a non‑linear skb backed by a splice‑imported file page. This flaw can be exploited to tamper with bridge traffic, potentially enabling ARP spoofing or denial‑of‑service attacks. The issue is actively exploited (CISA KEV).

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Authoritative CVE Metadata - CVSS Base Score: 8.8 (HIGH) - Published: 2026-06-25T09:16:44.643 - Last Modified: 2026-09-19T04:17:53.580

[!CAUTION] Known Exploited Vulnerability: YES (CISA KEV Added: 2026-09-18)

Original Description: 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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