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Fencer Vulns
medium 5.5

CVE-2023-53477 json

ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

published 2025-10-01 13 mo ago modified 2026-11-05 3 d ago also EUVD-2025-32762

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 5%
public exploits
0
none known

Summary

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

ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

In function rt6_nlmsg_size(), the length of nexthop is calculated by multipling the nexthop length of fib6_info and the number of siblings. However if the fib6_info has no lwtunnel but the siblings have lwtunnels, the nexthop length is less than it should be, and it will trigger a warning in inet6_rt_notify() as follows:

WARNING: CPU: 0 PID: 6082 at net/ipv6/route.c:6180 inet6_rt_notify+0x120/0x130 ...... Call Trace: <TASK> fib6_add_rt2node+0x685/0xa30 fib6_add+0x96/0x1b0 ip6_route_add+0x50/0xd0 inet6_rtm_newroute+0x97/0xa0 rtnetlink_rcv_msg+0x156/0x3d0 netlink_rcv_skb+0x5a/0x110 netlink_unicast+0x246/0x350 netlink_sendmsg+0x250/0x4c0 sock_sendmsg+0x66/0x70 ___sys_sendmsg+0x7c/0xd0 __sys_sendmsg+0x5d/0xb0 do_syscall_64+0x3f/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc

This bug can be reproduced by script:

ip -6 addr add 2002::2/64 dev ens2 ip -6 route add 100::/64 via 2002::1 dev ens2 metric 100

for i in 10 20 30 40 50 60 70; do ip link add link ens2 name ipv_$i type ipvlan ip -6 addr add 2002::$i/64 dev ipv_$i ifconfig ipv_$i up done

for i in 10 20 30 40 50 60; do ip -6 route append 100::/64 encap ip6 dst 2002::$i via 2002::1 dev ipv_$i metric 100 done

ip -6 route append 100::/64 via 2002::1 dev ipv_70 metric 100

This patch fixes it by adding nexthop_len of every siblings using rt6_nh_nlmsg_size().

Patch / fix

  • Linux Linux 5.4.235, 5.10.173, 5.15.100, 6.1.18, 6.2.5, 6.3
  • linux Debian 14, Debian 13, Debian 12 6.1.20-1

debian advisories DEBIAN-CVE-2023-53477

  • linux Ubuntu 20.04 LTS 5.4.0-152.169
  • linux Ubuntu 22.04 LTS 5.15.0-79.86
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1104.112
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1042.47
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1107.116
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1039.47
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1039.44
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1051.56

ubuntu advisories UBUNTU-CVE-2023-53477

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 9 5.14.0-362.8.1.el9_3
  • rv RHEL 9 5.14.0-362.8.1.el9_3
  • perf RHEL 9 5.14.0-362.8.1.el9_3
  • rtla RHEL 9 5.14.0-362.8.1.el9_3
  • bpftool RHEL 9 7.2.0-362.8.1.el9_3
  • libperf RHEL 9 5.14.0-362.8.1.el9_3
  • kernel-rt RHEL 9 5.14.0-362.8.1.el9_3
  • kernel-64k RHEL 9 5.14.0-362.8.1.el9_3

red hat advisories RHSA-2023:6583

  • kernel-syms SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 4.12.14-122.280.1
  • kernel-source SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 4.12.14-122.280.1
  • kernel-default SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS, SLE Live Patching 12 SP5 4.12.14-122.280.1
  • kgraft-patch-SLE12-SP5_Update_74 SLE Live Patching 12 SP5 1-8.5.1

suse advisories SUSE-SU-2025:4189-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-53477 updated cvss 6.0

kernel: ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 10 kernel
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3 d ago

Exploit prediction

0.16% chance of exploitation in the next 30 days, higher than 5% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.