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net/packet: guard the ll header push in packet_rcv_spkt()

Assessment

Severity
Moderate
CVSS base score
4.4CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Impact
Not stated
EPSS, next 30 days
Not scored yet
Public exploit code
No Nuclei template lists it
Exploitability
Not assessed
Publicly disclosed
No
Customer action
Required: apply the update
Component
Mariner
Weakness
—
Issued by
Linux
Published
25 Oct 2026 · October 2026
Last revised
26 Oct 2026Information published.
CVSS 3.1 base metricsRed raises the risk · green lowers it
Attack vector
LocalAV:L
Attack complexity
LowAC:L
Privileges required
HighPR:H
User interaction
NoneUI:N
Scope
UnchangedS:U
Confidentiality
NoneC:N
Integrity
NoneI:N
Availability
HighA:H

Updates that fix it

0 KBs

No KB listed

MSRC lists no downloadable update, which usually means a service-side fix or a release-notes update. Check the MSRC advisory.

Affected products

1 affected product
  • azl3 kernel 6.6.157.1-1 on Azure Linux 3.0
Page history

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Cite this version
Field-level log (0)

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Explore global source statements, affected packages and advisory history for CVE-2026-99033. The catalog has a separate collection scope from Microsoft release records.

Collected exploitation and prediction evidence

Risk source coverage

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

cve-program · CVE-2026-99033

Published

net/packet: guard the ll header push in packet_rcv_spkt()

In the Linux kernel, the following vulnerability has been resolved: net/packet: guard the ll header push in packet_rcv_spkt() packet_rcv_spkt() restores the link layer header with skb_push(skb, skb->data - skb_mac_header(skb)); That subtraction is only meaningful when the device actually has a link layer header. packet_rcv() and tpacket_rcv() both wrap it in dev_has_header(), which is also the predicate the block comment at the top of the file states the restore in terms of; packet_rcv_spkt() does not. commit d549699048b4 ("net/packet: fix packet receive on L3 devices without visible hard header") introduced the helper and changed the two call sites, and this one stayed behind. A device without a visible ll header can leave skb->mac_header at the 0xFFFF sentinel that __alloc_skb() initialises it to. A CAN skb does: init_can_skb() sets pkt_type and ip_summed but does not reset the headers, and commit 9f10374bb024 ("can: remove private CAN skb headroom infrastructure") dropped the skb_reset_*_header() calls that used to be there. skb_mac_header() is then 0xFFFF, the length becomes a large negative number and skb_push() reports it through skb_under_panic() -- from softirq context, so it is a full system panic even with panic_on_oops=0: skbuff: skb_under_panic: text:ffffffff8bd21bc1 len:-65455 put:-65471 head:... data:... tail:0x50 end:0x180 dev:can0 kernel BUG at net/core/skbuff.c:214! RIP: 0010:skb_panic+0x50/0x60 Call Trace: <IRQ> skb_push+0x38/0x40 packet_rcv_spkt+0xe1/0x170 __netif_receive_skb_core.constprop.0+0x7e8/0xd30 ... Kernel panic - not syncing: Fatal exception in interrupt The socket type is reachable: packet_create() accepts SOCK_PACKET alongside SOCK_RAW and SOCK_DGRAM behind the same CAP_NET_RAW check, and neither the socket length nor a capability check keeps it away from a CAN interface. The missing skb_reset_*_header() calls in init_can_skb() are a regression in their own right and are being fixed separately, but a packet socket should not turn a link layer that did not initialise its mac header into a kernel panic. Guard the push the way the other two receive paths do. Tested on v7.3-rc5 under QEMU with a slcan device on a pty, which is the driver RX path: vcan does not reproduce it, because can_send() resets the headers on the way out. One SOCK_PACKET socket bound to can0 and one frame written into the line discipline panics an unpatched kernel with the trace above; the same image with this patch prints no panic and powers off normally. Both kernels are this tree, defconfig plus CONFIG_CAN_SLCAN=y, differing only in this hunk.

Source published
23 Oct 2026 12:21:37 UTC
Source modified
23 Oct 2026 12:21:37 UTC
Observed here
23 Oct 2026 16:01:20 UTC
Source terms
CVE Program Terms of Use

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Sources read 28 Oct 02:54 UTC · 272 of 272 readable · 270 fully read · documentation 469/469 current