CVE-2024-50045 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
netfilter: br_netfilter: fix panic with metadata_dst skb
Fix a kernel panic in the br_netfilter module when sending untagged traffic via a VxLAN device. This happens during the check for fragmentation in br_nf_dev_queue_xmit.
It is dependent on: 1) the br_netfilter module being loaded; 2) net.bridge.bridge-nf-call-iptables set to 1; 3) a bridge with a VxLAN (single-vxlan-device) netdevice as a bridge port; 4) untagged frames with size higher than the VxLAN MTU forwarded/flooded
When forwarding the untagged packet to the VxLAN bridge port, before the netfilter hooks are called, br_handle_egress_vlan_tunnel is called and changes the skb_dst to the tunnel dst. The tunnel_dst is a metadata type of dst, i.e., skb_valid_dst(skb) is false, and metadata->dst.dev is NULL.
Then in the br_netfilter hooks, in br_nf_dev_queue_xmit, there's a check for frames that needs to be fragmented: frames with higher MTU than the VxLAN device end up calling br_nf_ip_fragment, which in turns call ip_skb_dst_mtu.
The ip_dst_mtu tries to use the skb_dst(skb) as if it was a valid dst with valid dst->dev, thus the crash.
This case was never supported in the first place, so drop the packet instead.
PING 10.0.0.2 (10.0.0.2) from 0.0.0.0 h1-eth0: 2000(2028) bytes of data. [ 176.291791] Unable to handle kernel NULL pointer dereference at
virtual address 0000000000000110 [ 176.292101] Mem abort info:
[ 176.292184] ESR = 0x0000000096000004
[ 176.292322] EC = 0x25: DABT (current EL), IL = 32 bits
[ 176.292530] SET = 0, FnV = 0
[ 176.292709] EA = 0, S1PTW = 0
[ 176.292862] FSC = 0x04: level 0 translation fault
[ 176.293013] Data abort info:
[ 176.293104] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[ 176.293488] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 176.293787] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 176.293995] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000043ef5000
[ 176.294166] [0000000000000110] pgd=0000000000000000,
p4d=0000000000000000 [ 176.294827] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[ 176.295252] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel veth
br_netfilter bridge stp llc ipv6 crct10dif_ce [ 176.295923] CPU: 0 PID: 188 Comm: ping Not tainted
6.8.0-rc3-g5b3fbd61b9d1 #2 [ 176.296314] Hardware name: linux,dummy-virt (DT)
[ 176.296535] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS
BTYPE=--) [ 176.296808] pc : br_nf_dev_queue_xmit+0x390/0x4ec [br_netfilter]
[ 176.297382] lr : br_nf_dev_queue_xmit+0x2ac/0x4ec [br_netfilter]
[ 176.297636] sp : ffff800080003630
[ 176.297743] x29: ffff800080003630 x28: 0000000000000008 x27:
ffff6828c49ad9f8 [ 176.298093] x26: ffff6828c49ad000 x25: 0000000000000000 x24:
00000000000003e8 [ 176.298430] x23: 0000000000000000 x22: ffff6828c4960b40 x21:
ffff6828c3b16d28 [ 176.298652] x20: ffff6828c3167048 x19: ffff6828c3b16d00 x18:
0000000000000014 [ 176.298926] x17: ffffb0476322f000 x16: ffffb7e164023730 x15:
0000000095744632 [ 176.299296] x14: ffff6828c3f1c880 x13: 0000000000000002 x12:
ffffb7e137926a70 [ 176.299574] x11: 0000000000000001 x10: ffff6828c3f1c898 x9 :
0000000000000000 [ 176.300049] x8 : ffff6828c49bf070 x7 : 0008460f18d5f20e x6 :
f20e0100bebafeca [ 176.300302] x5 : ffff6828c7f918fe x4 : ffff6828c49bf070 x3 :
0000000000000000 [ 176.300586] x2 : 0000000000000000 x1 : ffff6828c3c7ad00 x0 :
ffff6828c7f918f0 [ 176.300889] Call trace:
[ 176.301123] br_nf_dev_queue_xmit+0x390/0x4ec [br_netfilter]
[ 176.301411] br_nf_post_routing+0x2a8/0x3e4 [br_netfilter]
[ 176.301703] nf_hook_slow+0x48/0x124
[ 176.302060] br_forward_finish+0xc8/0xe8 [bridge]
[ 176.302371] br_nf_hook_thresh+0x124/0x134 [br_netfilter]
[ 176.302605] br_nf_forward_finish+0x118/0x22c [br_netfilter]
[ 176.302824] br_nf_forward_ip.part.0+0x264/0x290 [br_netfilter]
[ 176.303136] br_nf_forward+0x2b8/0x4e0 [br_netfilter]
[ 176.303359] nf_hook_slow+0x48/0x124
[ 176.303
---truncated---
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Analysis
by VulDB Data Team • 03/23/2026
The vulnerability CVE-2024-50045 affects the Linux kernel and specifically targets the br_netfilter module, which is part of the netfilter framework used for packet filtering and manipulation in bridged networks. This issue arises during the handling of untagged traffic forwarded through VxLAN devices, leading to a kernel panic due to a NULL pointer dereference. The root cause lies in how the kernel processes packets that exceed the VxLAN MTU, particularly when these packets are routed through a bridge configured with the br_netfilter module loaded and net.bridge.bridge-nf-call-iptables set to 1. When such packets are processed, the br_handle_egress_vlan_tunnel function modifies the skb_dst to point to a tunnel destination, which is a metadata type of destination that lacks a valid dev pointer, thereby causing a crash when subsequent netfilter hooks attempt to access the destination information.
The technical flaw manifests in the br_nf_dev_queue_xmit function where a check for fragmentation occurs, triggering br_nf_ip_fragment which subsequently calls ip_skb_dst_mtu. This function attempts to access the skb_dst(skb) as if it were a valid destination with a proper dev field, but since the tunnel_dst is a metadata type with dev set to NULL, the kernel crashes upon dereferencing a NULL pointer at virtual address 0x0000000000000110. This behavior aligns with CWE-476, which describes NULL pointer dereference, and represents a critical flaw in kernel memory management that can lead to system instability and potential denial of service. The ATT&CK framework would categorize this as a privilege escalation or denial of service technique, as it can be exploited to crash the kernel and render the system non-functional.
The operational impact of this vulnerability is significant for network environments that utilize bridging with VxLAN tunneling and netfilter functionality. Systems running Linux kernels with br_netfilter loaded and configured for bridge netfilter calls are at risk when handling large untagged packets that exceed VxLAN MTU limits. This scenario commonly occurs in virtualized environments, container orchestration platforms, and network infrastructure where VxLAN is used for overlay networking. The vulnerability can be triggered by simple network traffic patterns, making it particularly dangerous as it requires minimal conditions for exploitation. The kernel panic results in immediate system instability, potentially causing service disruption and requiring system reboot to restore functionality. Organizations using Linux-based networking equipment, cloud platforms, or virtualized infrastructures that rely on bridge and VxLAN configurations should prioritize patching to mitigate this risk.
The fix implemented addresses the root cause by dropping packets that would otherwise trigger the crash, rather than attempting to process them through the broken code path. This approach aligns with security best practices by ensuring system stability over attempting to support unsupported configurations. The solution prevents the kernel from entering an invalid state when encountering metadata_dst skb objects that lack proper device information, thus maintaining system integrity. This mitigation strategy is consistent with the principle of least privilege and fail-safe design, where the system gracefully handles unexpected conditions rather than attempting to process them through potentially flawed code paths. The patch ensures that such packets are dropped at the appropriate layer, preventing the NULL pointer dereference while maintaining the overall functionality of the network stack. Organizations should update their Linux kernel versions to include this fix and verify that their bridge configurations do not inadvertently create conditions that could trigger this vulnerability.