CVE-2026-98306
Received Received - Intake

IPv4 Socket Lookup Issue in Linux Kernel SRv6 Decapsulation

Publication date: 2026-10-06

Last updated on: 2026-10-06

Assigner: kernel.org

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.

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Meta Information

Published
2026-10-06
Last Modified
2026-10-06
Generated
2026-10-06
AI Q&A
2026-10-06
EPSS Evaluated
N/A
NVD
CVE-2026-98306
EUVD
EUVD-2026-93291

Affected Vendors & Products

Showing 9 associated CPEs
Vendor Product Version / Range
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 891ef8dd2a8d14e4e73a81dcdb135b574c57f556
Linux Linux 4.14

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves incorrect handling of the IPSKB_L3SLAVE flag during IPv4 decapsulation in SRv6 packets. When a packet arrives on an interface enslaved to a VRF, the flag should be set but was not, causing decapsulated packets to be incorrectly routed or dropped during socket lookup. This affects packet delivery to local sockets bound to the enslaved interface.

Detection Guidance

This vulnerability affects SRv6 packet handling in the Linux kernel, specifically related to VRF interfaces and IPIP decapsulation. Detection requires checking kernel logs for SRv6-related errors or misrouted packets on VRF-enslaved interfaces. Monitor for packets failing to reach intended sockets due to incorrect IPSKB_L3SLAVE flag handling.

Impact Analysis

If you use Linux with SRv6 and VRF configurations, this vulnerability could cause decapsulated packets to be misrouted or not delivered to intended local sockets. For example, a UDP socket bound to an enslaved interface may not receive decapsulated packets, while unbound sockets outside the VRF would. This disrupts expected network behavior and could lead to service disruptions.

Mitigation Strategies

Apply the kernel patch referenced in the CVE description (commit 44930446dde4). Update to a Linux kernel version that includes this fix. Verify the patch by checking if IPSKB_L3SLAVE is properly set during IPIP decapsulation on VRF interfaces.

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