Linux Kernel
CVE-2024-35888
HIGH
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
ERSPAN tunnel configuration mandatory on target raises AC to High; AV:N and PR:N as attacker sends network packets; C:L for uninitialized heap read, A:L for potential crash, no integrity impact.
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:
erspan: make sure erspan_base_hdr is present in skb->head
syzbot reported a problem in ip6erspan_rcv() [1]
Issue is that ip6erspan_rcv() (and erspan_rcv()) no longer make sure erspan_base_hdr is present in skb linear part (skb->head) before getting @ver field from it.
Add the missing pskb_may_pull() calls.
v2: Reload iph pointer in erspan_rcv() after pskb_may_pull() because skb->head might have changed.
[1]
BUG: KMSAN: uninit-value in pskb_may_pull_reason include/linux/skbuff.h:2742 [inline] BUG: KMSAN: uninit-value in pskb_may_pull include/linux/skbuff.h:2756 [inline] BUG: KMSAN: uninit-value in ip6erspan_rcv net/ipv6/ip6_gre.c:541 [inline] BUG: KMSAN: uninit-value in gre_rcv+0x11f8/0x1930 net/ipv6/ip6_gre.c:610 pskb_may_pull_reason include/linux/skbuff.h:2742 [inline] pskb_may_pull include/linux/skbuff.h:2756 [inline] ip6erspan_rcv net/ipv6/ip6_gre.c:541 [inline] gre_rcv+0x11f8/0x1930 net/ipv6/ip6_gre.c:610 ip6_protocol_deliver_rcu+0x1d4c/0x2ca0 net/ipv6/ip6_input.c:438 ip6_input_finish net/ipv6/ip6_input.c:483 [inline] NF_HOOK include/linux/netfilter.h:314 [inline] ip6_input+0x15d/0x430 net/ipv6/ip6_input.c:492 ip6_mc_input+0xa7e/0xc80 net/ipv6/ip6_input.c:586 dst_input include/net/dst.h:460 [inline] ip6_rcv_finish+0x955/0x970 net/ipv6/ip6_input.c:79 NF_HOOK include/linux/netfilter.h:314 [inline] ipv6_rcv+0xde/0x390 net/ipv6/ip6_input.c:310 __netif_receive_skb_one_core net/core/dev.c:5538 [inline] __netif_receive_skb+0x1da/0xa00 net/core/dev.c:5652 netif_receive_skb_internal net/core/dev.c:5738 [inline] netif_receive_skb+0x58/0x660 net/core/dev.c:5798 tun_rx_batched+0x3ee/0x980 drivers/net/tun.c:1549 tun_get_user+0x5566/0x69e0 drivers/net/tun.c:2002 tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048 call_write_iter include/linux/fs.h:2108 [inline] new_sync_write fs/read_write.c:497 [inline] vfs_write+0xb63/0x1520 fs/read_write.c:590 ksys_write+0x20f/0x4c0 fs/read_write.c:643 __do_sys_write fs/read_write.c:655 [inline] __se_sys_write fs/read_write.c:652 [inline] __x64_sys_write+0x93/0xe0 fs/read_write.c:652 do_syscall_64+0xd5/0x1f0 entry_SYSCALL_64_after_hwframe+0x6d/0x75
Uninit was created at: slab_post_alloc_hook mm/slub.c:3804 [inline] slab_alloc_node mm/slub.c:3845 [inline] kmem_cache_alloc_node+0x613/0xc50 mm/slub.c:3888 kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:577 __alloc_skb+0x35b/0x7a0 net/core/skbuff.c:668 alloc_skb include/linux/skbuff.h:1318 [inline] alloc_skb_with_frags+0xc8/0xbf0 net/core/skbuff.c:6504 sock_alloc_send_pskb+0xa81/0xbf0 net/core/sock.c:2795 tun_alloc_skb drivers/net/tun.c:1525 [inline] tun_get_user+0x209a/0x69e0 drivers/net/tun.c:1846 tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048 call_write_iter include/linux/fs.h:2108 [inline] new_sync_write fs/read_write.c:497 [inline] vfs_write+0xb63/0x1520 fs/read_write.c:590 ksys_write+0x20f/0x4c0 fs/read_write.c:643 __do_sys_write fs/read_write.c:655 [inline] __se_sys_write fs/read_write.c:652 [inline] __x64_sys_write+0x93/0xe0 fs/read_write.c:652 do_syscall_64+0xd5/0x1f0 entry_SYSCALL_64_after_hwframe+0x6d/0x75
CPU: 1 PID: 5045 Comm: syz-executor114 Not tainted 6.9.0-rc1-syzkaller-00021-g962490525cff #0
AnalysisAI
Uninitialized memory read in the Linux kernel's ERSPAN IPv6 receive path exposes kernel heap contents and may trigger a denial of service on systems acting as ERSPAN monitoring endpoints. Affected kernels fail to call pskb_may_pull() before accessing erspan_base_hdr in ip6erspan_rcv() and erspan_rcv(), allowing a network-adjacent attacker to cause reads from uninitialized socket buffer memory. No public exploit code exists and the EPSS score of 0.01% (1st percentile) reflects negligible observed exploitation interest; this is not listed in the CISA KEV catalog.
Technical ContextAI
ERSPAN (Encapsulated Remote SPAN) is a Cisco-originated protocol that tunnels mirrored network traffic inside GRE, commonly used in network monitoring architectures. The Linux kernel implements IPv6 ERSPAN receive handling in net/ipv6/ip6_gre.c (ip6erspan_rcv) and IPv4 in net/ipv4/ip_gre.c (erspan_rcv). Linux socket buffers (skbs) may be non-linear: headers can reside outside the contiguous skb->head region in paged fragments. The pskb_may_pull() function is the mandatory gate that linearizes a specified number of bytes into skb->head before header pointer arithmetic is safe; omitting it on the erspan_base_hdr structure allows the ver field to be read from uninitialized or arbitrary memory. The syzbot fuzzer caught this via KMSAN (Kernel Memory Sanitizer) producing an uninit-value report at net/ipv6/ip6_gre.c:541 during GRE packet ingestion. CWE-908 (Use of Uninitialized Resource) precisely describes the root cause: a resource is allocated and accessed before its relevant region is initialized or confirmed present in the linear buffer.
RemediationAI
Apply the upstream fix via the Linux kernel stable tree; eight patch commits are available at https://git.kernel.org/stable/c/06a939f72a24a7d8251f84cf4c042df86c6666ac and seven additional stable-branch commits (0ac328a5, 17af4205, 1db7fcb2, 4e3fdeec, b14b9f95, e54a0c79, ee008810). Debian users should apply updates through official security channels once the distribution packages the fix. An exact patched release version number was not independently confirmable from the provided reference data - verify with your distribution's security tracker. If patching is not immediately feasible and ERSPAN is not operationally required, remove ERSPAN tunnel interfaces (ip link del erspan0) or prevent module loading (echo 'install ip6_gre /bin/false' >> /etc/modprobe.d/blacklist.conf) as a compensating control; this disables all GRE-based tunneling, which will disrupt legitimate ERSPAN monitoring. Alternatively, firewall rules blocking IP protocol 47 (GRE) on external interfaces reduce exposure with the trade-off of breaking all GRE traffic.
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