# CVE-2026-99088: net: openvswitch: validate transport header presence in set_ipv6_addr

CVE-2026-99088 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99088, released October 27, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-99088
- Priority: Routine
- CVSS: 2.3 (Low)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 26, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99088

## Description

In the Linux kernel, the following vulnerability has been resolved:  net: openvswitch: validate transport header presence in set_ipv6_addr  When executing IPv6 address rewrite actions on IPv6 fragments, set_ipv6_addr() calls update_ipv6_checksum(). If parse_ipv6hdr() processes a non-first IPv6 fragment, it sets key->ip.proto to NEXTHDR_FRAGMENT and returns early without calling skb_set_transport_header().  update_ipv6_checksum() unconditionally evaluates skb_transport_offset() on entry before checking l4_proto.  Because skb->transport_header is uninitialized, this triggers a warning under CONFIG_DEBUG_NET=y although it is completely harmless.  Fix this by returning early in update_ipv6_checksum() if l4_proto is NEXTHDR_FRAGMENT. This avoids reading the uninitialized transport offset for fragments while preserving the debug warning for any other protocol where the transport header is unexpectedly missing.  See the syzbot trace:  !skb_transport_header_was_set(skb) WARNING: ./include/linux/skbuff.h:3075 at skb_transport_header include/linux/skbuff.h:3075 [inline], CPU#1: syz-executor463/5635 WARNING: ./include/linux/skbuff.h:3075 at skb_transport_offset include/linux/skbuff.h:3250 [inline], CPU#1: syz-executor463/5635 WARNING: ./include/linux/skbuff.h:3075 at update_ipv6_checksum net/openvswitch/actions.c:361 [inline], CPU#1: syz-executor463/5635 WARNING: ./include/linux/skbuff.h:3075 at set_ipv6_addr+0x462/0x660 net/openvswitch/actions.c:399, CPU#1: syz-executor463/5635 [...] RIP: 0010:skb_transport_header include/linux/skbuff.h:3075 [inline] RIP: 0010:skb_transport_offset include/linux/skbuff.h:3250 [inline] RIP: 0010:update_ipv6_checksum net/openvswitch/actions.c:361 [inline] RIP: 0010:set_ipv6_addr+0x462/0x660 net/openvswitch/actions.c:399 [...] Call Trace:  <TASK>  set_ipv6 net/openvswitch/actions.c:531 [inline]  do_execute_actions+0x557e/0x8600 net/openvswitch/actions.c:1366  ovs_execute_actions+0xde/0x520 net/openvswitch/actions.c:1592  ovs_packet_cmd_execute+0xb4f/0xf10 net/openvswitch/datapath.c:705  genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114  genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209  netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2572  genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218  netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1361  netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1916  sock_sendmsg_nosec+0x14e/0x190 net/socket.c:800

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.113-1 | [DEBIAN-CVE-2026-99088](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99088.md) | Oct 27, 2026 |
| Linux | linux Debian 14 | 7.2.11-1 | [DEBIAN-CVE-2026-99088](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99088.md) | Oct 27, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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