CVE-2026-98306 seg6: set IPSKB_L3SLAVE from IP6SKB_L3SLAVE on IPIP decapsulation
Missing VRF flag in SRv6 decapsulation allows packets to bypass VRF isolation, potentially exposing data to sockets outside the intended network namespace.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98306?
CVE-2026-98306 is a vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
seg6: set IPSKB_L3SLAVE from IP6SKB_L3SLAVE on IPIP decapsulation
When an SRv6 packet arrives on an interface enslaved to a VRF, vrf_ip6_rcv() sets IP6SKB_L3SLAVE in IP6CB, but decap_and_validate() has never set IPSKB_L3SLAVE in IPCB. The bit stayed clear in the common case, and with CONFIG_IPV6_MIP6 the leftover frag_max_size of a reassembled outer packet could even set it, with no VRF involved. Commit 44930446dde4 ("ipv6: seg6: clear IPv4 control block on IPIP decapsulation") then made the unreliable bit reliably clear.
The effect of the missing flag is visible with End.DX4 when a delivery to a local address of the node reaches the socket lookup. For example, a UDP socket bound to the enslaved ingress interface does not receive any of the decapsulated packets, while an unbound socket outside the VRF does. This contradicts Documentation/networking/vrf.rst: by default the scope of an unbound UDP or TCP socket is limited to the default VRF.
Set IPSKB_L3SLAVE for IPv4 in decap_and_validate(), which already does the same for IPv6. The socket lookup then matches the decapsulated packet like any other packet received on that enslaved interface. Such a packet matches an unbound UDP or TCP socket only when udp_l3mdev_accept or tcp_l3mdev_accept is set.
Which versions are affected by CVE-2026-98306?
How do I fix CVE-2026-98306?
Apply the vendor's patch.
Is CVE-2026-98306 being exploited?
There is no known exploitation of CVE-2026-98306 in the wild and no public exploit code.
Sources
Also known as AZL-106272, BELL-CVE-2026-98306, DEBIAN-CVE-2026-98306, GHSA-8vq5-3gc9-33qh, UBUNTU-CVE-2026-98306.