As Bot also suggested, Xubuntu would be your ideal distro in terms of performance, out of the two you mentioned.
But of course, personal preferences also come into play...
On Xubuntu vs Kubuntu/Ubuntu for your hardware
For a Core 2 Duo, 4 GB RAM and an old Radeon HD 2400,
Xubuntu (XFCE) is indeed usually the lightest of the three:
- Xubuntu (XFCE)
- Lowest RAM usage at idle in most cases.
- Very light on CPU and GPU effects.
- Good match for old hardware that you want to keep feeling “snappy”.
- Kubuntu (Plasma)
- Heavier than XFCE but quite efficient for a full‑featured DE.
- You’re already happy with its performance, which is a good sign.
- Ubuntu (GNOME)
- Typically the heaviest of the three in RAM and GPU usage.
- Might still be usable, but you will feel your 4 GB limit sooner, especially with a few browser tabs open.
So if
performance is your top priority,
Xubuntu is a very good suggestion. If you like Plasma’s features and can accept a bit more overhead than XFCE,
sticking with Kubuntu is also a solid choice for that laptop.
If you mainly like the
GNOME-style workflow (single top bar, app grid, etc.), you can get something similar on:
- Xubuntu: with GNOME‑like themes and a single top panel + Whisker menu / app grid.
- Kubuntu: by using a single panel and an “Application Dashboard”/GNOME‑like launcher.
This way, you keep performance closer to Xubuntu/Kubuntu levels instead of going to full GNOME.
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Security: Ubuntu 24 LTS vs Ubuntu 25
On the security side, there are two different things:
- Underlying security model (kernel, AppArmor, snap sandboxing, etc.).
- User‑visible tools like the “Security” app you mention.
Some points to keep in mind:
- LTS (e.g. 24.04)
- Gets long-term security updates and backported fixes.
- More conservative stack; fewer big changes during its lifetime.
- If a serious exploit is found (in the updater or anything else), this is the version most likely to receive a timely patch.
- Interim (e.g. 25.x)
- Newer kernel, GNOME/Plasma, and security features.
- May include new desktop security UX like the app you mentioned (per‑app file access prompts, improved portals, etc.).
- Shorter support period and more frequent changes.
I can’t verify the exact “Security app” feature set in Ubuntu 25 or confirm that it will always prompt for Firefox accessing your home directory – my knowledge stops before that release. If that feature exists and you like that behaviour, it’s a
point in favour of Ubuntu 25, but I wouldn’t choose it
only on that basis.
From a pure
risk management perspective on an old laptop:
- If you want maximum stability and long-term patches: prefer 24.04 LTS (Xubuntu/Kubuntu/Ubuntu).
- If you want to try the newer security UI/features and don’t mind being on a shorter‑lived release: test 25.x from a live USB and see if it runs well.
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About your “red team exploit” in the Update app
I can’t verify your specific finding, but in general:
- If your red team has found a real exploit in Ubuntu’s updater or related tooling, you should report it privately to Canonical (Ubuntu’s security team). That’s the best way to get it fixed and protect other users.
- Whether it affects 24, 25, or both depends entirely on the exact bug and code path – that’s impossible to judge without details, and it’s not something I can safely speculate about.
- If it is a genuine vulnerability, LTS releases normally get patches quickly once the vendor is informed.
So, instead of assuming “24 = insecure, 25 = secure”, it’s safer to:
- Keep whichever version you use fully updated.
- Report the issue to Canonical so both 24 and 25 can be patched if needed.
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Practical recommendation for your laptop
Given everything (performance + security):
- If you want the best performance on that hardware:
- Xubuntu 24.04 LTS (or 25.x if you test it and it runs well).
- Or stay on Kubuntu (which you already find fast) and tune effects down.
- If you really want GNOME and the new security UX:
- Try Ubuntu 25.x live and compare performance with your current Kubuntu.
- Check whether the security prompts work the way you expect.
- Whatever you choose:
- Keep it fully patched.
- If your red team exploit is real, responsibly disclose it to Ubuntu’s security team.
In short: for that specific laptop, I’d lean toward
Xubuntu or Kubuntu 24.04 LTS for a balance of performance and long‑term security, and only move to Ubuntu 25 GNOME if you confirm via live testing that the performance and security features meet your needs.
