In the Linux kernel, the following vulnerability has been resolved:
net: drop bad gso csum_start and offset in virtio_net_hdr
Tighten csum_start and csum_offset checks in virtio_net_hdr_to_skb for GSO packets.
The function already checks that a checksum requested with VIRTIO_NET_HDR_F_NEEDS_CSUM is in skb linear. But for GSO packets this might not hold for segs after segmentation.
Syzkaller demonstrated to reach this warning in skb_checksum_help
offset = skb_checksum_start_offset(skb); ret = -EINVAL; if (WARN_ON_ONCE(offset >= skb_headlen(skb)))
By injecting a TSO packet:
WARNING: CPU: 1 PID: 3539 at net/core/dev.c:3284 skb_checksum_help+0x3d0/0x5b0 ip_do_fragment+0x209/0x1b20 net/ipv4/ip_output.c:774 ip_finish_output_gso net/ipv4/ip_output.c:279 [inline] __ip_finish_output+0x2bd/0x4b0 net/ipv4/ip_output.c:301 iptunnel_xmit+0x50c/0x930 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x2296/0x2c70 net/ipv4/ip_tunnel.c:813 __gre_xmit net/ipv4/ip_gre.c:469 [inline] ipgre_xmit+0x759/0xa60 net/ipv4/ip_gre.c:661 __netdev_start_xmit include/linux/netdevice.h:4850 [inline] netdev_start_xmit include/linux/netdevice.h:4864 [inline] xmit_one net/core/dev.c:3595 [inline] dev_hard_start_xmit+0x261/0x8c0 net/core/dev.c:3611 __dev_queue_xmit+0x1b97/0x3c90 net/core/dev.c:4261 packet_snd net/packet/af_packet.c:3073 [inline]
The geometry of the bad input packet at tcp_gso_segment:
[ 52.003050][ T8403] skb len=12202 headroom=244 headlen=12093 tailroom=0 [ 52.003050][ T8403] mac=(168,24) mac_len=24 net=(192,52) trans=244 [ 52.003050][ T8403] shinfo(txflags=0 nr_frags=1 gso(size=1552 type=3 segs=0)) [ 52.003050][ T8403] csum(0x60000c7 start=199 offset=1536 ip_summed=3 complete_sw=0 valid=0 level=0)
Mitigate with stricter input validation.
csum_offset: for GSO packets, deduce the correct value from gso_type. This is already done for USO. Extend it to TSO. Let UFO be: udp[46]_ufo_fragment ignores these fields and always computes the checksum in software.
csum_start: finding the real offset requires parsing to the transport header. Do not add a parser, use existing segmentation parsing. Thanks to SKB_GSO_DODGY, that also catches bad packets that are hw offloaded. Again test both TSO and USO. Do not test UFO for the above reason, and do not test UDP tunnel offload.
GSO packet are almost always CHECKSUM_PARTIAL. USO packets may be CHECKSUM_NONE since commit 10154dbded6d6 ("udp: Allow GSO transmit from devices with no checksum offload"), but then still these fields are initialized correctly in udp4_hwcsum/udp6_hwcsum_outgoing. So no need to test for ip_summed == CHECKSUM_PARTIAL first.
This revises an existing fix mentioned in the Fixes tag, which broke small packets with GSO offload, as detected by kselftests.
CVSS Details
- CVSS 3.1 Base Score: 7.8
- CVSS 3.1 Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade kernel-tools-develUpgrade perfUpgrade kernel-debuginfo-common-aarch64Upgrade perf-debuginfoUpgrade kernel-develUpgrade kernel-toolsUpgrade kernel-tools-debuginfoUpgrade bpftoolUpgrade python-perfUpgrade kernelUpgrade kernel-livepatch-5.15.167-112.165Upgrade kernel-headersUpgrade kernel-debuginfoUpgrade python-perf-debuginfoUpgrade bpftool-debuginfoUpgrade kernel-debuginfo-common-x86_64 | May 20, 2026 | May 20, 2026 |
| Amazon_linux_2023 | — | Upgrade bpftool-debuginfoUpgrade kernel-debuginfo-common-x86_64Upgrade kernel-modules-extra-commonUpgrade kernel-modules-extraUpgrade kernel-livepatch-6.1.109-118.189Upgrade perf-debuginfoUpgrade python3-perf-debuginfoUpgrade kernel-toolsUpgrade kernel-tools-debuginfoUpgrade kernel-debuginfoUpgrade kernel-tools-develUpgrade kernelUpgrade python3-perfUpgrade kernel-develUpgrade kernel-debuginfo-common-aarch64Upgrade kernel-libbpf-develUpgrade perfUpgrade bpftoolUpgrade kernel-headersUpgrade kernel-libbpfUpgrade kernel-libbpf-static | Oct 16, 2025 | Aug 26, 2024 |
| Debian | — | Upgrade linuxUpgrade linux-6.1 | Sep 2, 2024 | Aug 26, 2024 |
| Oracle_linux | — | Upgrade kernel-uek | Nov 21, 2024 | Aug 26, 2024 |
| Suse | — | Upgrade dlm-kmp-64kbUpgrade kernel-default-livepatchUpgrade kernel-docs-htmlUpgrade reiserfs-kmp-rtUpgrade dtb-apmUpgrade kernel-rt_debug-develUpgrade kernel-source-vanillaUpgrade kernel-rt_debug-vdsoUpgrade cluster-md-kmp-azureUpgrade dtb-appleUpgrade kernel-rt-livepatch-develUpgrade dtb-amazonUpgrade kernel-debug-livepatch-develUpgrade cluster-md-kmp-defaultUpgrade kernel-default-extraUpgrade kernel-kvmsmall-vdsoUpgrade kernel-source-azureUpgrade kernel-zfcpdumpUpgrade dlm-kmp-defaultUpgrade dtb-amdUpgrade dtb-freescaleUpgrade gfs2-kmp-64kbUpgrade dtb-renesasUpgrade gfs2-kmp-rtUpgrade kernel-64kbUpgrade kernel-default-baseUpgrade dtb-hisiliconUpgrade kernel-kvmsmall-livepatch-develUpgrade kernel-azure-extraUpgrade kernel-syms-rtUpgrade dtb-alteraUpgrade kernel-rt_debug-livepatch-develUpgrade kernel-azure-optionalUpgrade reiserfs-kmp-64kbUpgrade dtb-broadcomUpgrade ocfs2-kmp-azureUpgrade ocfs2-kmp-rtUpgrade kernel-default-livepatch-develUpgrade kernel-symsUpgrade kernel-obs-qaUpgrade kernel-azure-vdsoUpgrade kernel-default-develUpgrade reiserfs-kmp-defaultUpgrade dtb-socionextUpgrade kselftests-kmp-rtUpgrade ocfs2-kmp-64kbUpgrade kernel-rt_debugUpgrade dtb-lgUpgrade kernel-rt-optionalUpgrade kernel-rt-vdsoUpgrade dtb-marvellUpgrade kernel-64kb-optionalUpgrade kernel-debugUpgrade dtb-amlogicUpgrade kernel-azureUpgrade kernel-source-rtUpgrade kernel-kvmsmall-develUpgrade kernel-debug-develUpgrade kernel-64kb-livepatch-develUpgrade kselftests-kmp-azureUpgrade dlm-kmp-azureUpgrade kernel-rt-develUpgrade kernel-default-base-rebuildUpgrade kernel-default-optionalUpgrade dtb-armUpgrade kselftests-kmp-64kbUpgrade kselftests-kmp-defaultUpgrade cluster-md-kmp-64kbUpgrade reiserfs-kmp-azureUpgrade dtb-xilinxUpgrade kernel-syms-azureUpgrade kernel-sourceUpgrade kernel-defaultUpgrade kernel-64kb-extraUpgrade kernel-debug-vdsoUpgrade kernel-rtUpgrade kernel-devel-azureUpgrade kernel-64kb-develUpgrade kernel-azure-develUpgrade kernel-devel-rtUpgrade dtb-allwinnerUpgrade kernel-docsUpgrade dtb-nvidiaUpgrade dlm-kmp-rtUpgrade kernel-default-vdsoUpgrade gfs2-kmp-defaultUpgrade cluster-md-kmp-rtUpgrade kernel-rt-livepatchUpgrade dtb-sprdUpgrade dtb-qcomUpgrade kernel-kvmsmallUpgrade gfs2-kmp-azureUpgrade kernel-macrosUpgrade kernel-obs-buildUpgrade dtb-rockchipUpgrade kernel-develUpgrade dtb-exynosUpgrade dtb-caviumUpgrade kernel-rt-extraUpgrade dtb-mediatekUpgrade kernel-azure-livepatch-develUpgrade ocfs2-kmp-default | Dec 5, 2025 | Sep 10, 2024 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Jan 20, 2025 | Aug 26, 2024 |
Prioritise with Active Threat Intelligence
With curated Threat Intelligence, you can see which vulnerabilities truly put you at risk, prioritize what matters most, and act before attackers do.
Explore Intelligence Hub