Background: I remember at my old place of employment how the web server admin would always make me change the httpd-accessible file upload directories so that they were owned by apache:apache or nobody:nobody.
He said this was for security reasons.
Question: Can you tell me what specifically were the security implications of this? Also is there a way to get apache to run as nobody:nobody, and are there security implications for that as well?
TIA
This is the wrong site for this question. Ordinarily you would not want the source code to be owned by the same user as Apache. Should a security flaw in Apache or your server-side scripts arise, an attacker could maliciously modify your web site's files without privilege escalation.
The one exception would be file upload directories, as you said. In this case, you want Apache to make changes to that directory.
There is a valid reason, supposing the httpd (Apache) was owned by root and belongs to the group root also, and that there was a vulnerability that was found in the code itself, for example, a malicious user requested a URL that is longer than expected and the httpd seg-faulted. Now, that exploit has uncovered root access which means, it has control over the system and hence a malicious user would ultimately seize control and create havoc on the box.
That is a reason why the ownership of the httpd daemon runs under nobody:nobody or apache:apache. It is effectively a preventative measure to ensure that no exploit/vulnerability will expose root access. Imagine the security implications if that was to happen.
Fortunately, now, depending on the Linux distribution, BSD variants (OpenBSD/FreeBSD/NetBSD) or the commercial Unix variants, the httpd daemon runs under a user group that has the least privileges. And furthermore, it would be safe to say that a lot of the Apache code has been well tested enough and stable. About 49% of servers across all domains are running Apache. Microsoft's IIS runs at 29% of the domains. This is according the the netcraft survey site here.
In another context, it shows that having a program running under least privileges would be deemed 'safe' and mitigates any possible chances of exploits, vulnerabilites.
Hope this helps, Best regards, Tom.