CVE-2026-97612

net: mpls: clear inner_protocol when the last label is popped

Published Sep 25, 2026 CVSS 3.1 · 7.8 High EPSS < 1% KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:

net: mpls: clear inner_protocol when the last label is popped

skb_mpls_push() records the pre-encapsulation network header once, gated
on !skb->inner_protocol. skb_mpls_pop() never clears that record, so it
outlives the encapsulation it describes.

Open vSwitch can then re-push MPLS onto a packet whose
inner_network_header still points at the older, deeper offset: push a
label, pop every label, recirculate (ovs_flow_key_update() re-derives
key->eth.type and resets network_header, but leaves inner_*), then push
again. ovs_fragment() trusts the record:

skb->network_header = skb->inner_network_header;

so skb_network_offset() goes negative. The bound check is signed:

if (skb_network_offset(skb) > MAX_L2_LEN)

a negative offset passes it, and prepare_frag() widens the value:

unsigned int hlen = skb_network_offset(skb);
memcpy(&data->l2_data, skb->data, hlen);

which is a ~4GiB memcpy out of a 30-byte per-CPU buffer.

Reproduced on v7.3-rc1. RDX is the truncated length, (unsigned int)(-8):

BUG: unable to handle page fault for address: ffffe8ffffc16000
#PF: supervisor write access in kernel mode
Oops: 0002 [#1] SMP KASAN NOPTI
RIP: 0010:memcpy+0x8/0x20
RDX: 00000000fffffff8 RSI: ffff888105d732db RDI: ffffe8ffffc16000
prepare_frag+0x3df/0x4e0
ovs_fragment+0x589/0x7e0
do_output+0x4ce/0x5e0
do_execute_actions+0x55d2/0x7b30
ovs_execute_actions+0xea/0x450

Same root-cause shape as commit 975b5b067f52 ("ipv6: sr: restore network
header before routing and forwarding"): a stale network header offset
reaching a consumer that widens it. Here it originates in the MPLS
push/pop path.

Clear inner_protocol once the packet is no longer MPLS, so a later push
re-records the current header. net/sched/act_mpls.c is the only other
skb_mpls_pop() caller and gets the same fix; sch_frag.c saves and
restores inner_protocol around fragmentation in the same way OVS does.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4817-1 linux-6.12 security update
Debian DLA Debian DLA DLA-4841-1 linux security update
Debian DSA Debian DSA DSA-6528-1 linux security update
Ubuntu USN Ubuntu USN USN-8961-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9019-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-9020-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9022-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9023-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9024-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9025-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9026-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-9029-1 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-9039-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-9040-1 Linux kernel (Low Latency NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-9066-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-9091-1 Linux kernel (NVIDIA Tegra) vulnerabilities
History
Type Values Removed Values Added
Weaknesses CWE-119
CWE-665
Type Values Removed Values Added
Weaknesses CWE-119
CWE-665
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: net: mpls: clear inner_protocol when the last label is popped skb_mpls_push() records the pre-encapsulation network header once, gated on !skb->inner_protocol. skb_mpls_pop() never clears that record, so it outlives the encapsulation it describes. Open vSwitch can then re-push MPLS onto a packet whose inner_network_header still points at the older, deeper offset: push a label, pop every label, recirculate (ovs_flow_key_update() re-derives key->eth.type and resets network_header, but leaves inner_*), then push again. ovs_fragment() trusts the record: skb->network_header = skb->inner_network_header; so skb_network_offset() goes negative. The bound check is signed: if (skb_network_offset(skb) > MAX_L2_LEN) a negative offset passes it, and prepare_frag() widens the value: unsigned int hlen = skb_network_offset(skb); memcpy(&data->l2_data, skb->data, hlen); which is a ~4GiB memcpy out of a 30-byte per-CPU buffer. Reproduced on v7.3-rc1. RDX is the truncated length, (unsigned int)(-8): BUG: unable to handle page fault for address: ffffe8ffffc16000 #PF: supervisor write access in kernel mode Oops: 0002 [#1] SMP KASAN NOPTI RIP: 0010:memcpy+0x8/0x20 RDX: 00000000fffffff8 RSI: ffff888105d732db RDI: ffffe8ffffc16000 prepare_frag+0x3df/0x4e0 ovs_fragment+0x589/0x7e0 do_output+0x4ce/0x5e0 do_execute_actions+0x55d2/0x7b30 ovs_execute_actions+0xea/0x450 Same root-cause shape as commit 975b5b067f52 ("ipv6: sr: restore network header before routing and forwarding"): a stale network header offset reaching a consumer that widens it. Here it originates in the MPLS push/pop path. Clear inner_protocol once the packet is no longer MPLS, so a later push re-records the current header. net/sched/act_mpls.c is the only other skb_mpls_pop() caller and gets the same fix; sch_frag.c saves and restores inner_protocol around fragmentation in the same way OVS does.
Title net: mpls: clear inner_protocol when the last label is popped
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 19, 2026, 9:10 AM
Reserved
Sep 24, 2026, 4:01 PM
Status
Received
Published
Sep 25, 2026, 11:17 AM
Modified
Oct 19, 2026, 10:17 AM
Severity
Moderate
Public date
Sep 25, 2026, 12:00 AM