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CVE-2026-53266
netfilter: bridge: make ebt_snat ARP rewrite writable
Published 2026-06-25 (4 months ago) by the Linux kernel CNA. Subsystem net/bridge. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-53266 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4665-1 · 2026-07-03 · text | 6.1.176-1 | Update the kernel and reboot. DLA-4665-1 shipped the fix on 2026-07-03, in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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().
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/bridge/netfilter/ebt_snat.c
- What this is
- NETFILTERMAINTAINERS section matched on net/*/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- ebt_snat
Check it on the machine
grep -wE 'CONFIG_BRIDGE|CONFIG_BRIDGE_EBT_SNAT|CONFIG_NETFILTER' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w ebt_snatPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_BRIDGE, CONFIG_BRIDGE_EBT_SNAT, CONFIG_NETFILTER
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Known to be exploited in the wild
- Added to KEV
- 2026-09-18
- Federal due date
- 2026-09-21
- Ransomware use
- unknown
- 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.
Signals
- Published
- 2026-06-25 (4 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.83%, higher than 56.7% of all CVEssource
- CISA KEV
- listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/bridge
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.10 | 5.10.259 | bf84ad7c7a9e |
| 5.10 | 5.15.210 | 76280b78cc9f |
| 5.10 | 6.1.176 | b7e91939ba9b |
| 5.10 | 6.6.143 | afd64b59c3de |
| 5.10 | 6.12.94 | 153ea96c806a |
| 5.10 | 6.18.36 | b18675263db1 |
| 5.10 | 7.0.13 | c9b5ff59feff |
| 5.10 | 7.1 | 67ba971ae025 |
| 5.4.73 | 0 | 0 |
| 5.8.17 | 0 | 0 |
| 5.9.2 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4671-1 | 2026-07-05 | bullseye 6.1.176-1~deb11u1 | tracker |
| DLA-4665-1 | 2026-07-03 | bookworm 6.1.176-1 | tracker |
| DLA-4664-1 | 2026-07-03 | bullseye 5.10.259-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- Exploitation requires local control of bridge/ebtables configuration and arranging an skb with shared non-linear backing memory; remote ARP traffic alone cannot create the splice-backed page condition.
- AC:LAttack complexity, low
- There is no race or rare external timing condition; the attacker can control the rule, ARP frame layout, and shared-frag setup needed to reach the write.
- PR:LPrivileges required, low
- The ebtables rule path requires CAP_NET_ADMIN, but this is reachable with namespace-local privileges via user/network namespaces rather than requiring init-namespace root.
- UI:NUser interaction, none
- No victim action is required once the attacker can configure the namespace and send the crafted traffic through the bridge path.
- S:CScope, changed
- The bug can let namespace-local network privileges corrupt file-backed/page-cache memory outside the bridge/netfilter security boundary, plausibly crossing a sandbox or namespace boundary.
- C:HConfidentiality impact, high
- The shared-page corruption can be leveraged toward privilege escalation or code execution, which can expose high-value system data.
- I:HIntegrity impact, high
- skb_store_bits() writes attacker-chosen MAC bytes into shared backing pages, giving a controlled corruption primitive against file-backed memory.
- A:HAvailability impact, high
- Controlled corruption of shared/file-backed pages can damage critical files or executable contents and can be repeated to cause severe system availability impact.