Using old ubuntu with the newest k3s version, containers can't access the internet

[sides-flow]

Environmental Info:
K3s Version:

k3s version v1.25.7+k3s1 (f7c20e23)
go version go1.19.6

Node(s) CPU architecture, OS, and Version:

vagrant@vagrant:~$ uname -a
Linux vagrant 4.15.0-55-generic #60-Ubuntu SMP Tue Jul 2 18:22:20 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

vagrant@vagrant:~$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.2 LTS
Release:	18.04
Codename:	bionic

Cluster Configuration:
default k3s installation

Describe the bug:
I use MacOS to run a vagrant box of ubuntu 18.04. I install k3s inside the vagrant box.
When I create a pod in the k3s cluster inside the vagrant box, I can access the host (=vagrant) but not anything else outside the vagrant (not my Mac, and no internet services like google.com / 8.8.8.8).
After some debugging (with basically zero knowledge on how container networking works), I discovered that cni and flannel are somehow part of it, and I saw that the recent release changed something with flannel.
When I install k3s with INSTALL_K3S_VERSION=v1.24.11+k3s1, it all seems to work just as normal.

Steps To Reproduce:
Creating the vagrant box

vagrant init rezonanc-oxid/ubuntu-bionic-kernel-4.15
vagrant up

Connecting to the vagrant box & setup

vagrant ssh
# Inside the vagrant terminal:
curl -sfL https://get.k3s.io | sh -
sudo chmod 644 /etc/rancher/k3s/k3s.yaml # To use kubectl without sudo
kubectl get pods -A # Sanity

Creating a pod with shell

kubectl run bbp --image=radial/busyboxplus:curl -i --tty -- sh

Expected behavior:
Inside the shell of the bbp pod:

[ root@bbp:/ ]$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 56 data bytes
64 bytes from 8.8.8.8: seq=0 ttl=61 time=10.260 ms
64 bytes from 8.8.8.8: seq=1 ttl=61 time=17.567 ms
64 bytes from 8.8.8.8: seq=2 ttl=61 time=11.395 ms
^C
--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 10.260/13.074/17.567 ms

Actual behavior:

[ root@bbp:/ ]$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 56 data bytes
^C
--- 8.8.8.8 ping statistics ---
8 packets transmitted, 0 packets received, 100% packet loss
[ root@bbp:/ ]$

[brandond]

• Duplicate of Networking/NAT not working on older iptables versions with v1.25.7+k3s1 #7096

Please upgrade to the latest 1.25 release.

[sides-flow]

• Duplicate of Networking/NAT not working on older iptables versions with v1.25.7+k3s1 #7096

Please upgrade to the latest 1.25 release.

I just ran it again, with the steps above. It used this version:

vagrant@vagrant:~$ curl -sfL https://get.k3s.io | sh -
[INFO]  Finding release for channel stable
[INFO]  Using v1.25.7+k3s1 as release
[INFO]  Downloading hash https://github.com/k3s-io/k3s/releases/download/v1.25.7+k3s1/sha256sum-amd64.txt

Still the same behavior. However, when I install using this command:

vagrant@vagrant:~$ curl -sfL https://get.k3s.io | INSTALL_K3S_VERSION=v1.26.3+k3s1 sh -
[INFO]  Using v1.26.3+k3s1 as release
[INFO]  Downloading hash https://github.com/k3s-io/k3s/releases/download/v1.26.3+k3s1/sha256sum-amd64.txt

The problem is solved.
I guess it's better to update the stable channel to a more recent release that fixes this issue.
Anyways, this issue should be kept close since it shouldn't occur in future releases...