CVE-2024-36933

CVE-2024-36933 is a medium-severity vulnerability in Linux Linux Kernel with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-908.

Key facts

Description

In the Linux kernel, the following vulnerability has been resolved: nsh: Restore skb->{protocol,data,mac_header} for outer header in nsh_gso_segment(). syzbot triggered various splats (see [0] and links) by a crafted GSO packet of VIRTIO_NET_HDR_GSO_UDP layering the following protocols: ETH_P_8021AD + ETH_P_NSH + ETH_P_IPV6 + IPPROTO_UDP NSH can encapsulate IPv4, IPv6, Ethernet, NSH, and MPLS. As the inner protocol can be Ethernet, NSH GSO handler, nsh_gso_segment(), calls skb_mac_gso_segment() to invoke inner protocol GSO handlers. nsh_gso_segment() does the following for the original skb before calling skb_mac_gso_segment() 1. reset skb->network_header 2. save the original skb->{mac_heaeder,mac_len} in a local variable 3. pull the NSH header 4. resets skb->mac_header 5. set up skb->mac_len and skb->protocol for the inner protocol. and does the following for the segmented skb 6. set ntohs(ETH_P_NSH) to skb->protocol 7. push the NSH header 8. restore skb->mac_header 9. set skb->mac_header + mac_len to skb->network_header 10. restore skb->mac_len There are two problems in 6-7 and 8-9. (a) After 6 & 7, skb->data points to the NSH header, so the outer header (ETH_P_8021AD in this case) is stripped when skb is sent out of netdev. Also, if NSH is encapsulated by NSH + Ethernet (so NSH-Ethernet-NSH), skb_pull() in the first nsh_gso_segment() will make skb->data point to the middle of the outer NSH or Ethernet header because the Ethernet header is not pulled by the second nsh_gso_segment(). (b) While restoring skb->{mac_header,network_header} in 8 & 9, nsh_gso_segment() does not assume that the data in the linear buffer is shifted. However, udp6_ufo_fragment() could shift the data and change skb->mac_header accordingly as demonstrated by syzbot. If this happens, even the restored skb->mac_header points to the middle of the outer header. It seems nsh_gso_segment() has never worked with outer headers so far. At the end of nsh_gso_segment(), the outer header must be restored for the segmented skb, instead of the NSH header. To do that, let's calculate the outer header position relatively from the inner header and set skb->{data,mac_header,protocol} properly. [0]: BUG: KMSAN: uninit-value in ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline] BUG: KMSAN: uninit-value in ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline] BUG: KMSAN: uninit-value in ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668 ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline] ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline] ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668 ipvlan_start_xmit+0x5c/0x1a0 drivers/net/ipvlan/ipvlan_main.c:222 __netdev_start_xmit include/linux/netdevice.h:4989 [inline] netdev_start_xmit include/linux/netdevice.h:5003 [inline] xmit_one net/core/dev.c:3547 [inline] dev_hard_start_xmit+0x244/0xa10 net/core/dev.c:3563 __dev_queue_xmit+0x33ed/0x51c0 net/core/dev.c:4351 dev_queue_xmit include/linux/netdevice.h:3171 [inline] packet_xmit+0x9c/0x6b0 net/packet/af_packet.c:276 packet_snd net/packet/af_packet.c:3081 [inline] packet_sendmsg+0x8aef/0x9f10 net/packet/af_packet.c:3113 sock_sendmsg_nosec net/socket.c:730 [inline] __sock_sendmsg net/socket.c:745 [inline] __sys_sendto+0x735/0xa10 net/socket.c:2191 __do_sys_sendto net/socket.c:2203 [inline] __se_sys_sendto net/socket.c:2199 [inline] __x64_sys_sendto+0x125/0x1c0 net/socket.c:2199 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x63/0x6b Uninit was created at: slab_post_alloc_hook mm/slub.c:3819 [inline] slab_alloc_node mm/slub.c:3860 [inline] __do_kmalloc_node mm/slub.c:3980 [inline] __kmalloc_node_track_caller+0x705/0x1000 mm/slub.c:4001 kmalloc_reserve+0x249/0x4a0 net/core/skbuff.c:582 __ ---truncated---

Frequently asked questions

What is CVE-2024-36933?
In the Linux kernel, the following vulnerability has been resolved: nsh: Restore skb->{protocol,data,mac_header} for outer header in nsh_gso_segment(). syzbot triggered various splats (see [0] and links) by a crafted GSO packet of VIRTIO_NET_HDR_GSO_UDP layering the following protocols: ETH_P_8021AD + ETH_P_NSH + ETH_P_IPV6 + IPPROTO_UDP NSH can encapsulate IPv4, IPv6, Ethernet, NSH, and MPLS. As the inner protocol can be Ethernet, NSH GSO handler, nsh_gso_segment(), calls skb_mac_gso_segment() to invoke inner protocol GSO handlers. nsh_gso_segment() does the following for the original skb before calling skb_mac_gso_segment() 1. reset skb->network_header 2. save the original skb->{mac_heaeder,mac_len} in a local variable 3. pull the NSH header 4. resets skb->mac_header 5. set up skb->mac_len and skb->protocol for the inner protocol. and does the following for the segmented skb 6. set ntohs(ETH_P_NSH) to skb->protocol 7. push the NSH header 8. restore skb->mac_header 9. set skb->mac_header + mac_len to skb->network_header 10. restore skb->mac_len There are two problems in 6-7 and 8-9. (a) After 6 & 7, skb->data points to the NSH header, so the outer header (ETH_P_8021AD in this case) is stripped when skb is sent out of netdev. Also, if NSH is encapsulated by NSH + Ethernet (so NSH-Ethernet-NSH), skb_pull() in the first nsh_gso_segment() will make skb->data point to the middle of the outer NSH or Ethernet header because the Ethernet header is not pulled by the second nsh_gso_segment(). (b) While restoring skb->{mac_header,network_header} in 8 & 9, nsh_gso_segment() does not assume that the data in the linear buffer is shifted. However, udp6_ufo_fragment() could shift the data and change skb->mac_header accordingly as demonstrated by syzbot. If this happens, even the restored skb->mac_header points to the middle of the outer header. It seems nsh_gso_segment() has never worked with outer headers so far. At the end of nsh_gso_segment(), the outer header must be restored for the segmented skb, instead of the NSH header. To do that, let's calculate the outer header position relatively from the inner header and set skb->{data,mac_header,protocol} properly. [0]: BUG: KMSAN: uninit-value in ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline] BUG: KMSAN: uninit-value in ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline] BUG: KMSAN: uninit-value in ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668 ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline] ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline] ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668 ipvlan_start_xmit+0x5c/0x1a0 drivers/net/ipvlan/ipvlan_main.c:222 __netdev_start_xmit include/linux/netdevice.h:4989 [inline] netdev_start_xmit include/linux/netdevice.h:5003 [inline] xmit_one net/core/dev.c:3547 [inline] dev_hard_start_xmit+0x244/0xa10 net/core/dev.c:3563 __dev_queue_xmit+0x33ed/0x51c0 net/core/dev.c:4351 dev_queue_xmit include/linux/netdevice.h:3171 [inline] packet_xmit+0x9c/0x6b0 net/packet/af_packet.c:276 packet_snd net/packet/af_packet.c:3081 [inline] packet_sendmsg+0x8aef/0x9f10 net/packet/af_packet.c:3113 sock_sendmsg_nosec net/socket.c:730 [inline] __sock_sendmsg net/socket.c:745 [inline] __sys_sendto+0x735/0xa10 net/socket.c:2191 __do_sys_sendto net/socket.c:2203 [inline] __se_sys_sendto net/socket.c:2199 [inline] __x64_sys_sendto+0x125/0x1c0 net/socket.c:2199 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x63/0x6b Uninit was created at: slab_post_alloc_hook mm/slub.c:3819 [inline] slab_alloc_node mm/slub.c:3860 [inline] __do_kmalloc_node mm/slub.c:3980 [inline] __kmalloc_node_track_caller+0x705/0x1000 mm/slub.c:4001 kmalloc_reserve+0x249/0x4a0 net/core/skbuff.c:582 __ ---truncated---
How severe is CVE-2024-36933?
CVE-2024-36933 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2024-36933 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (20th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2024-36933?
CVE-2024-36933 primarily affects Linux Linux Kernel. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2024-36933?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2024-36933 have an EU (EUVD) identifier?
Yes. CVE-2024-36933 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2024-36283.
When was CVE-2024-36933 published?
CVE-2024-36933 was published on 2024-05-30 and last updated on 2026-06-17.

References

Affected products (8)

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