Linux Kernel
CVE-2024-26857
HIGH
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Uninit read yields confidentiality impact (C:L) and possible kernel instability (A:L); no demonstrated integrity impact, so I:N rather than NVD's I:L.
Primary rating from Vendor (416baaa9-dc9f-4396-8d5f-8c081fb06d67).
CVSS VectorVendor: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Lifecycle Timeline
7DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
geneve: make sure to pull inner header in geneve_rx()
syzbot triggered a bug in geneve_rx() [1]
Issue is similar to the one I fixed in commit 8d975c15c0cd ("ip6_tunnel: make sure to pull inner header in __ip6_tnl_rcv()")
We have to save skb->network_header in a temporary variable in order to be able to recompute the network_header pointer after a pskb_inet_may_pull() call.
pskb_inet_may_pull() makes sure the needed headers are in skb->head.
[1] BUG: KMSAN: uninit-value in IP_ECN_decapsulate include/net/inet_ecn.h:302 [inline] BUG: KMSAN: uninit-value in geneve_rx drivers/net/geneve.c:279 [inline] BUG: KMSAN: uninit-value in geneve_udp_encap_recv+0x36f9/0x3c10 drivers/net/geneve.c:391 IP_ECN_decapsulate include/net/inet_ecn.h:302 [inline] geneve_rx drivers/net/geneve.c:279 [inline] geneve_udp_encap_recv+0x36f9/0x3c10 drivers/net/geneve.c:391 udp_queue_rcv_one_skb+0x1d39/0x1f20 net/ipv4/udp.c:2108 udp_queue_rcv_skb+0x6ae/0x6e0 net/ipv4/udp.c:2186 udp_unicast_rcv_skb+0x184/0x4b0 net/ipv4/udp.c:2346 __udp4_lib_rcv+0x1c6b/0x3010 net/ipv4/udp.c:2422 udp_rcv+0x7d/0xa0 net/ipv4/udp.c:2604 ip_protocol_deliver_rcu+0x264/0x1300 net/ipv4/ip_input.c:205 ip_local_deliver_finish+0x2b8/0x440 net/ipv4/ip_input.c:233 NF_HOOK include/linux/netfilter.h:314 [inline] ip_local_deliver+0x21f/0x490 net/ipv4/ip_input.c:254 dst_input include/net/dst.h:461 [inline] ip_rcv_finish net/ipv4/ip_input.c:449 [inline] NF_HOOK include/linux/netfilter.h:314 [inline] ip_rcv+0x46f/0x760 net/ipv4/ip_input.c:569 __netif_receive_skb_one_core net/core/dev.c:5534 [inline] __netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5648 process_backlog+0x480/0x8b0 net/core/dev.c:5976 __napi_poll+0xe3/0x980 net/core/dev.c:6576 napi_poll net/core/dev.c:6645 [inline] net_rx_action+0x8b8/0x1870 net/core/dev.c:6778 __do_softirq+0x1b7/0x7c5 kernel/softirq.c:553 do_softirq+0x9a/0xf0 kernel/softirq.c:454 __local_bh_enable_ip+0x9b/0xa0 kernel/softirq.c:381 local_bh_enable include/linux/bottom_half.h:33 [inline] rcu_read_unlock_bh include/linux/rcupdate.h:820 [inline] __dev_queue_xmit+0x2768/0x51c0 net/core/dev.c:4378 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] kmem_cache_alloc_node+0x5cb/0xbc0 mm/slub.c:3903 kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:560 __alloc_skb+0x352/0x790 net/core/skbuff.c:651 alloc_skb include/linux/skbuff.h:1296 [inline] alloc_skb_with_frags+0xc8/0xbd0 net/core/skbuff.c:6394 sock_alloc_send_pskb+0xa80/0xbf0 net/core/sock.c:2783 packet_alloc_skb net/packet/af_packet.c:2930 [inline] packet_snd net/packet/af_packet.c:3024 [inline] packet_sendmsg+0x70c2/0x9f10 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
AnalysisAI
Uninitialized memory read in the Linux kernel's GENEVE (Generic Network Virtualization Encapsulation) driver allows a remote unauthenticated attacker to trigger information disclosure and potential kernel instability by sending crafted UDP encapsulated packets to a GENEVE endpoint. The vulnerability exists in geneve_rx() within drivers/net/geneve.c, where skb->network_header is not saved before pskb_inet_may_pull() is called; if that function reallocates the skb head, the stale pointer causes subsequent IP_ECN_decapsulate() to read uninitialized kernel memory. EPSS is low (0.25%, 16th percentile), and the flaw is not listed in CISA KEV, indicating no confirmed active exploitation at time of analysis.
Technical ContextAI
GENEVE is an overlay network tunneling protocol carried over UDP (typically port 6081), widely used in cloud and container networking environments including OpenStack Neutron and Kubernetes CNI plugins. The vulnerable code path is triggered during UDP receive processing: udp_rcv → geneve_udp_encap_recv → geneve_rx. The root cause (CWE-908: Use of Uninitialized Resource) is a missing network header pointer save-and-restore pattern around pskb_inet_may_pull(). This function may linearize or reallocate the socket buffer's head region, invalidating any previously cached pointer to skb->network_header. The analogous pattern was previously fixed for ip6_tunnel in commit 8d975c15c0cd. The syzbot KMSAN trace confirms uninitialized bytes are read in IP_ECN_decapsulate() at geneve.c:279. CPE data confirms the affected product is cpe:2.3:o:linux:linux_kernel covering multiple stable branches up through 6.8-rc3.
RemediationAI
Apply the kernel vendor patches available across multiple stable branches via the kernel.org stable git commits. The canonical fix commits are: https://git.kernel.org/stable/c/048e16dee1fc609c1c85072ccd70bfd4b5fef6ca, https://git.kernel.org/stable/c/0ece581d2a66e8e488c0d3b3e7b5760dbbfdbdd5, https://git.kernel.org/stable/c/1ca1ba465e55b9460e4e75dec9fff31e708fec74, https://git.kernel.org/stable/c/59d2a4076983303f324557a114cfd5c32e1f6b29, and four additional stable-series commits. Distribution users should apply the relevant kernel update from their vendor (e.g., Debian Security). As a compensating control where immediate patching is not feasible, unloading or blocking the geneve kernel module (rmmod geneve; echo 'install geneve /bin/true' >> /etc/modprobe.d/disable-geneve.conf) prevents the vulnerable code from executing, but will disable all GENEVE-based overlay networking - a significant trade-off in environments using Kubernetes VXLAN/GENEVE CNIs or OpenStack Neutron. Alternatively, firewall rules blocking inbound UDP port 6081 at the perimeter reduce external attack surface while preserving GENEVE for trusted internal traffic.
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External POC / Exploit Code
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