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bdu:2025-08092

EUVD-2026-245855

fkie_cve-2025-52890

Incus is a system container and virtual machine manager. When using an ACL on a device connected to a bridge, Incus versions 6.12 and 6.13generates nftables rules that partially bypass security options `security.mac_filtering`, `security.ipv4_filtering` and `security.ipv6_filtering`. This can lead to ARP spoofing on the bridge and to fully spoof another VM/container on the same bridge. Commit 254dfd2483ab8de39b47c2258b7f1cf0759231c8 contains a patch for the issue.

GHSA-p7fw-vjjm-2rwp — Incus creates nftables rules that partially bypass security options

Affected: Go: github.com/lxc/incus/v6

### Summary

When using an ACL on a device connected to a bridge, Incus generates nftables rules that partially bypass security options `security.mac_filtering`, `security.ipv4_filtering` and `security.ipv6_filtering`. This can lead to ARP spoofing on the bridge and to fully spoof another VM/container on the same bridge.

### Details

In commit d137a063c2fe2a6983c995ba75c03731bee1557d, a few rules in the bridge input chain are moved to the top of the chain:

ct state established,related accept

iifname "{{.hostName}}" ether type arp accept iifname "{{.hostName}}" ip6 nexthdr ipv6-icmp icmpv6 type { nd-neighbor-solicit, nd-neighbor-advert } accept

However, these rules accept packets that should be filtered and maybe dropped by later rules in the "MAC filtering", "IPv4 filtering" and "IPv6 filtering" snippets:

iifname "{{.hostName}}" ether type arp arp saddr ether != {{.hwAddr}} drop iifname "{{.hostName}}" ether type ip6 icmpv6 type 136 @nh,528,48 != {{.hwAddrHex}} drop ... iifname "{{.hostName}}" ether type arp arp saddr ip != { {{.ipv4NetsList}} } drop ... iifname "{{.hostName}}" ether type ip6 icmpv6 type 136 {{.ipv6NetsPrefixList}} drop

Basically, the added rules partially bypass the security options `security.mac_filtering`, `security.ipv4_filtering` and `security.ipv6_filtering`. Doing so, they allow an attacker to perform ARP poisoning/spoofing attacks and send malicious Neighbor Advertisement (type 136).

### PoC

With this terraform infr…

openSUSE-SU-2025:15317-1 — incus-6.14-1.1 on GA media

incus-6.14-1.1 on GA media

UBUNTU-CVE-2025-52890

Affected: Ubuntu:Pro:24.04:LTS: incus, Ubuntu:25.10: incus, Ubuntu:Pro:26.04:LTS: incus