CVE-2026-53266
netfilter: bridge: make ebt_snat ARP rewrite writable
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().
In plain language
AI Act nowCVE-2026-53266 is a serious Linux kernel flaw in systems missing the 5.5 or vendor-backported fix, and small businesses with affected servers should act urgently.
A local low-privileged attacker can exploit an out-of-bounds write (CWE-787) in Linux kernel bridge ebtables SNAT ARP rewriting, potentially escalating to full system compromise.
What to do now
- Check each Linux server's running kernel version and whether it uses bridge ebtables SNAT rules that rewrite ARP addresses.
- Install your Linux distributor's security kernel update containing the fix; upstream fixes are available in 5.5, 5.9, and 5.10.
- If an update cannot be installed immediately, disable affected ebtables SNAT ARP-rewrite rules and restrict untrusted local user access.
- Restart into the updated kernel and confirm the new version is running.
CVSS Vector Breakdown
AV:LAttack VectorAC:LAttack ComplexityPR:LPrivileges RequiredUI:NUser InteractionS:CScopeC:HConfidentialityI:HIntegrityA:HAvailabilityWeaknesses
Affected Products
Exploitability
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.
Attack Graph
Click technique nodes for MITRE ATT&CK details · drag to pan · Ctrl/⌘ + scroll to zoom, or go fullscreen.
MITRE ATT&CK
2 techniquesReferences
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