# CVE-2023-53343: icmp6: Fix null-ptr-deref of ip6_null_entry->rt6i_idev in icmp6_dev().

> A local attacker can cause a kernel crash by sending crafted IPv6 packets with specific extension headers, leading to a denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53343, DEBIAN-CVE-2023-53343, GHSA-wcr6-fh62-j9wm, UBUNTU-CVE-2023-53343

## What is CVE-2023-53343?

CVE-2023-53343 is a medium-severity vulnerability in Linux kernel, published on 17 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

icmp6: Fix null-ptr-deref of ip6_null_entry->rt6i_idev in icmp6_dev().

With some IPv6 Ext Hdr (RPL, SRv6, etc.), we can send a packet that
has the link-local address as src and dst IP and will be forwarded to
an external IP in the IPv6 Ext Hdr.

For example, the script below generates a packet whose src IP is the
link-local address and dst is updated to 11::.

  # for f in $(find /proc/sys/net/ -name *seg6_enabled*); do echo 1 > $f; done
  # python3
  >>> from socket import *
  >>> from scapy.all import *
  >>>
  >>> SRC_ADDR = DST_ADDR = "fe80::5054:ff:fe12:3456"
  >>>
  >>> pkt = IPv6(src=SRC_ADDR, dst=DST_ADDR)
  >>> pkt /= IPv6ExtHdrSegmentRouting(type=4, addresses=["11::", "22::"], segleft=1)
  >>>
  >>> sk = socket(AF_INET6, SOCK_RAW, IPPROTO_RAW)
  >>> sk.sendto(bytes(pkt), (DST_ADDR, 0))

For such a packet, we call ip6_route_input() to look up a route for the
next destination in these three functions depending on the header type.

  * ipv6_rthdr_rcv()
  * ipv6_rpl_srh_rcv()
  * ipv6_srh_rcv()

If no route is found, ip6_null_entry is set to skb, and the following
dst_input(skb) calls ip6_pkt_drop().

Finally, in icmp6_dev(), we dereference skb_rt6_info(skb)->rt6i_idev->dev
as the input device is the loopback interface.  Then, we have to check if
skb_rt6_info(skb)->rt6i_idev is NULL or not to avoid NULL pointer deref
for ip6_null_entry.

BUG: kernel NULL pointer dereference, address: 0000000000000000
 PF: supervisor read access in kernel mode
 PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 0 PID: 157 Comm: python3 Not tainted 6.4.0-11996-gb121d614371c #35
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
RIP: 0010:icmp6_send (net/ipv6/icmp.c:436 net/ipv6/icmp.c:503)
Code: fe ff ff 48 c7 40 30 c0 86 5d 83 e8 c6 44 1c 00 e9 c8 fc ff ff 49 8b 46 58 48 83 e0 fe 0f 84 4a fb ff ff 48 8b 80 d0 00 00 00 <48> 8b 00 44 8b 88 e0 00 00 00 e9 34 fb ff ff 4d 85 ed 0f 85 69 01
RSP: 0018:ffffc90000003c70 EFLAGS: 00000286
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 00000000000000e0
RDX: 0000000000000021 RSI: 0000000000000000 RDI: ffff888006d72a18
RBP: ffffc90000003d80 R08: 0000000000000000 R09: 0000000000000001
R10: ffffc90000003d98 R11: 0000000000000040 R12: ffff888006d72a10
R13: 0000000000000000 R14: ffff8880057fb800 R15: ffffffff835d86c0
FS:  00007f9dc72ee740(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000057b2000 CR4: 00000000007506f0
PKRU: 55555554
Call Trace:
 <IRQ>
 ip6_pkt_drop (net/ipv6/route.c:4513)
 ipv6_rthdr_rcv (net/ipv6/exthdrs.c:640 net/ipv6/exthdrs.c:686)
 ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:437 (discriminator 5))
 ip6_input_finish (./include/linux/rcupdate.h:781 net/ipv6/ip6_input.c:483)
 __netif_receive_skb_one_core (net/core/dev.c:5455)
 process_backlog (./include/linux/rcupdate.h:781 net/core/dev.c:5895)
 __napi_poll (net/core/dev.c:6460)
 net_rx_action (net/core/dev.c:6529 net/core/dev.c:6660)
 __do_softirq (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/irq.h:142 kernel/softirq.c:554)
 do_softirq (kernel/softirq.c:454 kernel/softirq.c:441)
 </IRQ>
 <TASK>
 __local_bh_enable_ip (kernel/softirq.c:381)
 __dev_queue_xmit (net/core/dev.c:4231)
 ip6_finish_output2 (./include/net/neighbour.h:544 net/ipv6/ip6_output.c:135)
 rawv6_sendmsg (./include/net/dst.h:458 ./include/linux/netfilter.h:303 net/ipv6/raw.c:656 net/ipv6/raw.c:914)
 sock_sendmsg (net/socket.c:725 net/socket.c:748)
 __sys_sendto (net/socket.c:2134)
 __x64_sys_sendto (net/socket.c:2146 net/socket.c:2142 net/socket.c:2142)
 do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
RIP: 0033:0x7f9dc751baea
Code: d8 64 89 02 48 c7 c0 ff f
---truncated---

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2023-53343?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53343?

Apply the vendor's patch.

## Is CVE-2023-53343 being exploited?

There is no known exploitation of CVE-2023-53343 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-53343 and fix it if it is affected.

What it is: CVE-2023-53343 is a medium-severity vulnerability in Linux kernel, published on 17 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-53343 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-53343/ (Markdown: https://insights.sbomify.com/CVE-2023-53343/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53343
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53343
- OSV: https://osv.dev/vulnerability/CVE-2023-53343

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53343/
Summaries are generated and may contain mistakes; the official description above is the record.