# CVE-2026-99033: net/packet: guard the ll header push in packet_rcv_spkt() CVE-2026-99033 is fixed in 19 products on 1 platform, first by DEBIAN-CVE-2026-99033, released October 24, 2026. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-99033 - Priority: Routine - CVSS: 4.4 (Moderate) - EPSS: 0.0019 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Oct 23, 2026 - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99033 ## Description 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: 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. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | bpftool6.12 amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | bpftool6.12-debuginfo amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel-livepatch-6.12.113-138.209 amzn 2023 | 1:1.0-0.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12 amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-debuginfo amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-debuginfo-common-aarch64 amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-debuginfo-common-x86_64 amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-devel amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-headers amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-modules-extra amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-modules-extra-common amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-tools amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-tools-debuginfo amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | kernel6.12-tools-devel amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | linux Debian 13.5 (trixie) | 6.12.113-1 | [DEBIAN-CVE-2026-99033](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99033.md) | Oct 24, 2026 | | Linux | linux Debian 14 | 7.2.11-1 | [DEBIAN-CVE-2026-99033](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99033.md) | Oct 24, 2026 | | Linux | perf6.12 amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | perf6.12-debuginfo amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | python3-perf6.12 amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | | Linux | python3-perf6.12-debuginfo amzn 2023 | 1:6.12.113-138.209.amzn2023 | [ALAS2023-2026-3335](https://patchblox.com/security/data/fix/linux/alas2023-2026-3335.md) | Nov 7, 2026 | --- Data as of 2026-11-08T19:12:23Z UTC. 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