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

Vulnerability summary

CVE-2026-53266 is a high (CVSS 8.8) Out-of-bounds Write vulnerability in Linux Kernel. It is known to be exploited: CISA lists it, first on 18-09-2026. EPSS estimates a 0.93% chance of exploitation in the next 30 days, higher than 60.8% of scored vulnerabilities.

Timeline

1. 25-06-2026
   PublishedVulnerability first disclosed.
2. 18-09-2026
   Added to CISA KEVExploitedLinux Kernel Out-of-Bounds Write Vulnerability
3. 19-09-2026
   Last modifiedVulnerability information updated.
4. 21-09-2026
   CISA remediation dueDeadline passedApply mitigations per vendor instructions.

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().

• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.