CVE-2023-52843

MEDIUM
Published May 21, 2024 Modified Sep 24, 2025 CWE-908

Description

In the Linux kernel, the following vulnerability has been resolved: llc: verify mac len before reading mac header LLC reads the mac header with eth_hdr without verifying that the skb has an Ethernet header. Syzbot was able to enter llc_rcv on a tun device. Tun can insert packets without mac len and with user configurable skb->protocol (passing a tun_pi header when not configuring IFF_NO_PI). BUG: KMSAN: uninit-value in llc_station_ac_send_test_r net/llc/llc_station.c:81 [inline] BUG: KMSAN: uninit-value in llc_station_rcv+0x6fb/0x1290 net/llc/llc_station.c:111 llc_station_ac_send_test_r net/llc/llc_station.c:81 [inline] llc_station_rcv+0x6fb/0x1290 net/llc/llc_station.c:111 llc_rcv+0xc5d/0x14a0 net/llc/llc_input.c:218 __netif_receive_skb_one_core net/core/dev.c:5523 [inline] __netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5637 netif_receive_skb_internal net/core/dev.c:5723 [inline] netif_receive_skb+0x58/0x660 net/core/dev.c:5782 tun_rx_batched+0x3ee/0x980 drivers/net/tun.c:1555 tun_get_user+0x54c5/0x69c0 drivers/net/tun.c:2002 Add a mac_len test before all three eth_hdr(skb) calls under net/llc. There are further uses in include/net/llc_pdu.h. All these are protected by a test skb->protocol == ETH_P_802_2. Which does not protect against this tun scenario. But the mac_len test added in this patch in llc_fixup_skb will indirectly protect those too. That is called from llc_rcv before any other LLC code. It is tempting to just add a blanket mac_len check in llc_rcv, but not sure whether that could break valid LLC paths that do not assume an Ethernet header. 802.2 LLC may be used on top of non-802.3 protocols in principle. The below referenced commit shows that used to, on top of Token Ring. At least one of the three eth_hdr uses goes back to before the start of git history. But the one that syzbot exercises is introduced in this commit. That commit is old enough (2008), that effectively all stable kernels should receive this.

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CVSS v3.1 Score

5.5
MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-908 CWE-908

Affected Products

Vendor Product
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel

References

Advisories & Patches

https://git.kernel.org/stable/c/0a720d0259ad3521ec6c9e4199f9f6fc75bac77a https://git.kernel.org/stable/c/352887b3edd007cf9b0abc30fe9d98622acd859b https://git.kernel.org/stable/c/3a2653828ffc6101aef80bf58d5b77484239f779 https://git.kernel.org/stable/c/7b3ba18703a63f6fd487183b9262b08e5632da1b https://git.kernel.org/stable/c/900a4418e3f66a32db6baaf23f92b99c20ae6535 https://git.kernel.org/stable/c/9a3f9054a5227d7567cba1fb821df48ccecad10c https://git.kernel.org/stable/c/cbdcdf42d15dac74c7287679fb2a9d955f8feb1f https://git.kernel.org/stable/c/f980e9a57dfb9530f1f4ee41a2420f2a256d7b29 https://git.kernel.org/stable/c/ff5cb6a4f0c6d7fbdc84858323fb4b7af32cfd79 https://git.kernel.org/stable/c/0a720d0259ad3521ec6c9e4199f9f6fc75bac77a https://git.kernel.org/stable/c/352887b3edd007cf9b0abc30fe9d98622acd859b https://git.kernel.org/stable/c/3a2653828ffc6101aef80bf58d5b77484239f779 https://git.kernel.org/stable/c/7b3ba18703a63f6fd487183b9262b08e5632da1b https://git.kernel.org/stable/c/900a4418e3f66a32db6baaf23f92b99c20ae6535 https://git.kernel.org/stable/c/9a3f9054a5227d7567cba1fb821df48ccecad10c https://git.kernel.org/stable/c/cbdcdf42d15dac74c7287679fb2a9d955f8feb1f https://git.kernel.org/stable/c/f980e9a57dfb9530f1f4ee41a2420f2a256d7b29 https://git.kernel.org/stable/c/ff5cb6a4f0c6d7fbdc84858323fb4b7af32cfd79

Frequently Asked Questions

What is CVE-2023-52843? +
In the Linux kernel, the following vulnerability has been resolved: llc: verify mac len before reading mac header LLC reads the mac header with eth_hdr without verifying that the skb has an Ethernet header. Syzbot was able to enter llc_rcv on a tun device. Tun can insert packets without mac len and with user configurable skb->protocol (passing a tun_pi header when not configuring IFF_NO_PI). BUG: KMSAN: uninit-value in llc_station_ac_send_test_r net/llc/llc_station.c:81 [inline] BUG: KMSAN: uninit-value in llc_station_rcv+0x6fb/0x1290 net/llc/llc_station.c:111 llc_station_ac_send_test_r net/llc/llc_station.c:81 [inline] llc_station_rcv+0x6fb/0x1290 net/llc/llc_station.c:111 llc_rcv+0xc5d/0x14a0 net/llc/llc_input.c:218 __netif_receive_skb_one_core net/core/dev.c:5523 [inline] __netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5637 netif_receive_skb_internal net/core/dev.c:5723 [inline] netif_receive_skb+0x58/0x660 net/core/dev.c:5782 tun_rx_batched+0x3ee/0x980 drivers/net/tun.c:1555 tun_get_user+0x54c5/0x69c0 drivers/net/tun.c:2002 Add a mac_len test before all three eth_hdr(skb) calls under net/llc. There are further uses in include/net/llc_pdu.h. All these are protected by a test skb->protocol == ETH_P_802_2. Which does not protect against this tun scenario. But the mac_len test added in this patch in llc_fixup_skb will indirectly protect those too. That is called from llc_rcv before any other LLC code. It is tempting to just add a blanket mac_len check in llc_rcv, but not sure whether that could break valid LLC paths that do not assume an Ethernet header. 802.2 LLC may be used on top of non-802.3 protocols in principle. The below referenced commit shows that used to, on top of Token Ring. At least one of the three eth_hdr uses goes back to before the start of git history. But the one that syzbot exercises is introduced in this commit. That commit is old enough (2008), that effectively all stable kernels should receive this. It has a CVSS v3.1 base score of 5.5 (MEDIUM).
How severe is CVE-2023-52843? +
CVE-2023-52843 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.
What products are affected by CVE-2023-52843? +
CVE-2023-52843 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2023-52843? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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