Sunday, November 12, 2017

The security blanket blues revisited, or: keeping your Power Mac safe in an Intel world

Way back in 2012 I wrote a fairly basic piece on Power Mac security, and ever since then I've promised repeatedly to do an update for what's happened in between. So here it is.

The usual advice well-meaning but annoying people will give us Power Mac users is, "there are many security holes in your machine, so you shouldn't ever use it on the Internet." The first part is true. The second part is, at least right now, not. You just have to understand where the vulnerabilities lie, patch the holes you can, and mitigate the vulnerabilities that you can't. However, doing so is absolutely imperative and absolutely your responsibility. If some easily remotely exploitable bug surfaces that cannot be mitigated or blocked, I'll change my tune here, but that's not presently the case.

The most important thing to keep in mind is that, as virtually all the regular readers of this blog know, Power Macs use a completely different architecture than the majority of what's out there today, and this has important security ramifications. The vast majority of presently extant low-level exploits like buffer overflows and use-after-frees broadly depend on being able to deposit Intel or ARM machine code in memory and have it executed by the victim application, but our instruction set and (often) memory layout are completely different, so any such exploit would have to be specific to PowerPC to successfully execute. At worst, an non-PowerPC exploit of this type would just crash the application or, in extreme cases, the machine. While the more security conscious amongst you will (correctly) point out this is a special example of "security by obscurity," that doesn't mean this heterogeneity isn't an advantage. Attackers go where the money is, and it's not our machines. No current Intel Mac can easily generate code that will run on a Power Mac without a lot of work either.

But our systems definitely do not sail above the fray. Where we are most practically vulnerable falls under two major categories: information leakage, and cross-platform attacks. In the first case, unsecured networking, weak encryption or other flaws could leak private data such as passwords, credentials or personal data from our computers to an attacker; in the worst case they could allow an attacker to masquerade as you to other services or sites. In the second case, applications on your computer could be duped into performing tasks on behalf of an attacker using a payload that is not specific to a particular machine type, but can run anywhere the cross-platform environment they utilize exists (such as Java, Flash, Microsoft Word macros, scripting languages like shell scripts, JavaScript, etc.) and is able to exploit flaws in that environment to take over any machine that can run the code. In the worst case, an attacker could gain administrator access and complete control of the system, and because the exploit is not architecture-dependent, we could potentially run the poisoned code too.

So as promised, here's an updated practical guide to keeping your beloved Power Mac safe, or at least safer, today 11 years and nine operating system releases after the last Power Mac rolled off the assembly line. This post is hardly comprehensive and you should not assume it covers all relevant deficiencies, but, for the record, these are the recommendations I myself use on my own systems. I reference prior blog posts here you can read for more details, but this guide will cover the basic notions and try to give you an idea of priority. Please note: this document primarily applies to systems running 10.4 and later. The classic Mac OS through OS 9.2.2 has an extremely small attack surface because of its radically different architecture, and while browsers on OS 9 (including, though this is improving, Classilla) are subject to information leakage attacks and should not run Flash or Java, other kinds of attacks are almost impossible upon it. There are a few exceptions noted below. For 10.0 through 10.3, however, there are sadly much fewer good options for securing these systems, and I would simply advise putting them behind a good firewall and assuming everything you do on them is not secured.

Obviously, I also assume for the below that you're running the current version of TenFourFox and can securely download additional tools if necessary!

General recommendations

Make sure your clock is set correctly: certificate verification will fail if your clock is off more than a few minutes in either direction. Particularly on 10.4 systems (but also observed on 10.5), systems with long durations of uptime without sleeping or being shutdown may go out of synchronization with any time server you use. The first and easiest way to reestablish the connection to your timeserver is either by rebooting, or unchecking and then re-checking the time server checkbox in System Preferences. If your system is powered on and off regularly you may not have a need even to do this much. However, if this is insufficient and you are comfortable with the command line, you could try the more definitive solution in our article.

Consider using a non-admin account for basic activities: this will ensure that, if a old PowerPC-compatible exploit or Trojan horse is around and does get through, the damage is limited. At least one well-known OS X Trojan horse circulated in a PowerPC-compatible version as late as 2012!

Why do I have to enter my password? Consider this every time you're asked for it; a little paranoia is just good common sense. Ask yourself, does this application actually need administrative access? Or is this program doing something other than it claims?

Security issues with connectivity and networking

Built-in networking: On OS X, enable the built-in firewall in System Preferences (Sharing, Firewall) and enable stealth mode, and if you can, also Block UDP Traffic from the Advanced menu within that preference pane. This substantially reduces the surface for incoming network threats. Using a hardware firewall is even better, especially in combination, as well as disabling UPnP on your router if your applications don't require it; in fact, my personal daily drivers live on a specially secured wired network that cannot directly route to the Internet. There are a number of possible exploits in the network-accessible components of 10.4 and 10.5 and simply preventing access to them in this fashion is probably the best approach. Note that UDP is still necessary for some kinds of protocols such as local Windows file and printer sharing (in that case, blocking it at the router level rather on individual Macs would be more appropriate), and disabling UPnP may be problematic for some applications.

WiFi: All Power Macs are subject to the KRACK attack and there is no known client-side fix (more info). The problem can be mitigated by going into your router settings and selecting WPA2 (not just WPA!) AES-CCMP as your only means of Wi-Fi security, which some routers may abbreviate to just "AES." Do not use TKIP. Routers may also be vulnerable, particularly if your router is itself a client to another WiFi network such as being in repeater mode; you should check to see if a firmware update is available, and consider another router if necessary.

Although AES-CCMP is much more resistant to attacks than TKIP and an attacker cannot actually join a network secured with it, they could clone your access point to a second access point with the same SSID and MAC/BSSID on a different channel and entice you to transparently connect to that. This is not very likely in a controlled home environment, but it could be an issue for public Wi-Fi or close quarters like dorms or apartments. Immediately disable Wi-Fi if you see two copies of the same network; it could be an attempt to snare you. See our article for a more in-depth way of detecting such an attack.

If you are on a public Wi-Fi connection you can't control, you should assume your connection is completely insecure (the same applies for WEP, such as on Mac OS 9, which does not support WPA2 natively, or WPA). Use a VPN if you have it available, and/or only connect to secure hosts, such as over HTTPS and SSH, to layer your connection with a secondary level of encryption. A better browser can help ... like, I dunno, TenFourFox. Just a suggestion.

Bluetooth: All Power Macs are potentially vulnerable to BlueBorne-based attacks, though the practical likelihood of being exploited is low (more info). These attacks are generally low-level and would need to be specific to PowerPC to function, but could be a source of system instability if a malicious Bluetooth device is broadcasting poison packets with Intel or ARM code embedded in them. Keep Bluetooth off if you don't need it except in controlled environments; when tethering, if a malicious device is likely to be in range, Wi-Fi is probably safer even with the caveats above.

Hardening OS X

These are well-known vulnerabilities in OS X which can be, in some cases, exploited remotely.

sudo at the wrong time: Because a password is not required to change the system date and time (either with System Preferences or using systemsetup from the command line), an attacker can set the clock wrong and then dupe vulnerable versions of the sudo utility, which allows you to run commands with administrator permissions, to acquire that same administrative access without authentication. This is due to a convenience in sudo where repeated use within a certain interval does not require a password; thus, the simplest and most secure solution is to always require a password. Start a Terminal window (or start /Applications/Utilities/Terminal) and enter the following commands:

  • sudo visudo (enter your password)
  • Using the vi editor which then appears, add the line Defaults timestamp_timeout=0 at the end. If you don't know how to use vi, type these key strokes:

    • 0G (the number zero, and a capital G)
    • o (lower case "o")
    • Defaults timestamp_timeout=0
    • Press the ESCape key and then type :wq! (colon, lower case "w", lower case "q", exclamation point) and press ENTER.

If you get an error, you did it wrong; start over. See the original article for more information.

RootPipe/systemsetupusthebomb: This is an actual flaw in another privileged system component called writeconfig that can be exploited to write arbitrary files with root permissions, also giving an attacker administrative access. The simplest fix is to go to System Preferences, and under Security, check "Require password to unlock each secure system preference" (and make sure the lock at the lower left is locked). Now any known use of the vulnerable tool will either fail or at least prompt you for a password. This covers all known exploits for this component, but for a more comprehensive approach (that may have side effects), see the original article.

Shellshock: The version of the Bourne again shell (bash) that comes with all PowerPC versions of OS X is susceptible to Shellshock, a collection of methods of causing the shell to execute arbitrary commands passed to it through environment variables. Although of particular concern to anyone using their machine as a server, it is possible to use this exploit even on single-user systems in more limited circumstances. All versions prior to 4.3.30 are vulnerable. If you have never fixed this on your system, then download the patched version of bash 4.3.30 that we provide as a community service and follow these directions exactly:

  1. Put the file in your home directory and double-click to decompress it. You should be left with a file named bash-4.3.30-10.4u. Do not change the name.
  2. Close all terminal windows and programs if they are open, just to make sure you won't stomp on bash while a program is trying to call it. Start /Applications/Utilities/Terminal and have exactly one window open.
  3. In that Terminal window, type these commands exactly as shown. If you get any errors, STOP and ask for help.

    • exec tcsh
    • chmod +x bash-4.3.30-10.4u

      (IMPORTANT! If you replaced /bin/bash (and/or /bin/sh) with any earlier version using these commands, DO NOT ENTER THE NEXT TWO COMMANDS. If you have never replaced them, then do go ahead; these will put the old ones in a safe place just in case.)

    • sudo mv /bin/bash /bin/bash_old (enter your password)
    • sudo mv /bin/sh /bin/sh_old (enter your password; if you don't get prompted again, you need to fix sudo with the steps above!)

      Everybody does these:

    • sudo cp bash-4.3.30-10.4u /bin/bash (enter your password)
    • sudo cp bash-4.3.30-10.4u /bin/sh (enter your password)

  4. Restart your Mac as a paranoia to make sure everything is using the new copy of bash.

If you're not sure, bash --version will display what you're running (mine says GNU bash, version 4.3.30(5)-release (powerpc-apple-darwin8.11.0). The version we provide is universal and will work on PowerPC and Intel from 10.4 through at least 10.9. If you want to check if your version is correctly behaving, see the original article for a test battery.

Other vulnerabilities in OS X built-in software

Although there aren't updates for most of these, you should at least be aware of the actual risk, and how to reduce it.

Some of the entries in this and the following sections reference plugins. These are usually stored in /Library/Internet Plug-Ins, but there may be per-user plugins installed in Library/Internet Plug-Ins in your home folder. You can disable them as recommended below by simply moving them to another folder, or deleting them outright if appropriate.

Java: Java is not safe on Power Macs; all versions of Java provided on any PowerPC-compatible version of Mac OS or OS X have serious well-known vulnerabilities. In particular, exploits such as Flashback can obtain system access in a cross-platform fashion. If the Java plugin is on your computer, it should be removed or disabled (or use TenFourFox, natch, which won't even run it), and you should only run signed Java applets from trusted sources if you must run them at all.

QuickTime: There are historical PowerPC-based exploits for certain codecs in QuickTime, though none of these are known to be circulating now, and no specific PowerPC-based exploit is known for QT 7+ generally. (While QT 6.0.3 in OS 9/Classic is technically vulnerable, the limitations of OS 9 make the exploit difficult and it would have to be specific to both OS 9 and PowerPC.) It is possible for QuickTime playlists and certain other kinds of scriptable content to be used to load data over the network, but they can be only interacted with in limited ways, and to actually use them for executable data would require a PowerPC-compatible attack. While such an attack is feasible and possible, it isn't very likely to occur or succeed on a Power Mac. This mode of attack can be minimized further by removing or disabling the QuickTime Plugin (or use TenFourFox, natch, which won't even run it); removing the Plugin won't affect using the QuickTime Player.

Preview.app: Preview.app and the built-in image and PDF viewer libraries also have known holes, but no known specific PowerPC-based attacks which would be required to exploit them. The built-in PDF toolkit doesn't understand JavaScript in PDF files or embedded Flash, and as a result is much safer than using the real Adobe Acrobat Reader (which you should really only use for protected documents). If you don't mind the speed, you can also use the built-in PDF viewer in TenFourFox by going to Preferences, TenFourFox and checking the preference to enable it, though our internal viewer currently supports even fewer features than Preview. TenFourFox also can view many images by simply dragging them to any open browser window. Again, while an attack through a malicious image or PDF file is feasible and possible, it isn't very likely to occur or succeed on a Power Mac. This mode of attack can be minimized further by removing any Internet plugins that furnish PDF access in the browser, including and especially the Adobe Acrobat plugin (or use TenFourFox, natch, which doesn't even run them and implements its own sandboxed PDF viewer).

WebKit and Safari: Safari, and many other software packages, uses the version of WebKit on the system to render web pages and other network, HTML and image assets; it is, essentially, the built-in "WebKit shell." With the exception of OmniWeb, every PowerPC-compatible WebKit-based browser (Safari, iCab, Roccat, Stainless, Demeter, Shiira, etc.) relies on the version of WebKit the operating system provides, which means they inherit all the bugs and security issues of the built-in WebKit framework as well as any bugs in the shell they provide. (Gecko-based browsers bring their own libraries with them, but we're the only Gecko-based browser still updated for PowerPC OS X.)

I'm sure all of you are enthusiastic daily drivers of TenFourFox, but WebKit should also be updated because of how many other apps depend on it. For 10.5, of course, the best solution is Tobias' Leopard WebKit. Leopard WebKit not only includes a very current WebKit framework, but also includes an updated OS Security framework, and can relink WebKit shells and other programs using a provided utility.

Unfortunately, a similar supported option is not available for 10.4. TenFourKit, also written by Tobias, does update the system framework somewhat but does not include security or encryption updates, and has not received any updates since 2012; it's basically the same version as the framework built-in to the OmniWeb browser. For this reason, you should avoid Safari and other WebKit shell applications like iCab on 10.4, as they will not be sufficiently protected, and you should be cautious of apps that attempt to display web pages over the network since the vast majority will use the built-in WebKit also. Because the OS's security framework is also not current, many secure sites will either not connect properly, or throw inexplicable errors.

Currently all WebKit shells support, and will instantiate, plugins (TenFourFox doesn't). I still advise disabling them or removing them where appropriate, but if you can't do this, ClickToPlugin will at least reduce drive-by risk in Safari.

Mail.app: Mail uses the built-in system WebKit (as above), and may have other deficiencies which are not patched. These deficiencies likely require PowerPC-specific exploits, though Apple Mail's general lack of updates implies other vulnerabilities likely lurk such as information leaks and inadequate connection security. Although Tenfourbird (an unaffiliated project) was once a solid and secure alternative, it has not been maintained since version 38.9 as of this writing, so unfortunately I am no longer able to generally recommend it. The simplest and safest approach is simply to use a webmail service instead in TenFourFox or Leopard WebKit unless you absolutely must have a local mail client; in that case, I would use Tenfourbird over Apple Mail, since it is at least more up to date.

Major third-party and optional software vulnerabilities

Your web browser: Currently TenFourFox (10.4+), Leopard WebKit (10.5 only) and Roccat (10.5 only) are known to be updated on a semi-regular basis (we issue TenFourFox releases with security updates, updated certificates and pinned keys every six weeks simultaneously with Firefox ESR updates). No other browser is current, though at least a re-linked WebKit shell will have fewer vulnerabilities. Note that Roccat also needs to be relinked with Leopard WebKit for maximum security.

Flash: Flash is not safe on Power Macs; all PowerPC-compatible versions of Adobe Flash Player have serious well-known vulnerabilities. The cross-platform Rosetta Flash exploit is able to steal credentials and cookies with 10.1 and earlier versions of Flash, and the recommended server mitigation does not fix the problem in these versions (only Flash 10.2+). Furthermore, Flash applets have been previously demonstrated to attack network settings in a cross-platform fashion, and there are other sandbox escape vulnerabilities that have been reported. Although unofficial "later" versions of the Flash plugin have circulated for Power Macs, these are still Flash 10.1 internally with a bumped version number and do not actually have any fixes. Unless you have content that absolutely cannot be viewed without Flash, you should remove or disable the Flash plugin (or use TenFourFox, natch, which won't even run it); a tool like SandboxSafari or the experimental PopOut Player can help reduce the risk for legacy content that still requires it.

Microsoft Office and OpenOffice/NeoOffice/LibreOffice: None of these office applications is currently updated for Power Macs and all of them have potential vulnerabilities to Word and Excel macro viruses, though the OpenOffice derivatives are much less likely to be successfully exploited. For Word it is unlikely you will want macros enabled (and you should definitely turn them off in the preferences except for those rare situations in which they are needed), but this could be a real issue for Excel power users. Office v.X, and Office 98 in Classic/Mac OS 9, are probably too old to be effectively pwned, but many macro attacks against Office 2004 and 2008 will run on Power Macs and the Open XML Converter can be attacked in some of the same ways. Microsoft, damn their Redmond hides, does not offer any of the updaters prior to Office 2008 for download anymore, but I've archived some of them on the Gopher server. For Office 2008, start here (note that you may need to download earlier service packs, which are currently still available as of this writing). Note that Office 2008 cannot run Visual Basic for Applications (VBA), which is a drop in functionality but also a reduction in attack surface, nor can the OpenOffice alternatives. NeoOffice has not been updated for PowerPC in some time; 5.2.0alpha0 is the last version of LibreOffice for Power Macs and is generally my recommendation, but you can also download OpenOffice 4.0.0. All will run on 10.4+.

Note that while iWork/Numbers does support some Excel macros, it does not support VBA and seems to have some issues interpreting macros in general, so it is less likely to be exploited. The venerable AppleWorks nee ClarisWorks is also not known to have any serious vulnerabilities.

Adobe Acrobat and Adobe Acrobat Reader: Acrobat allows embedded Flash and JavaScript, which also makes it a scriptable cross-platform target, and Adobe Acrobat is no longer updated on PowerPC OS X. (The classic Mac OS version is less vulnerable because it implements less functionality, but it may have compatibility issues with more recent documents.) The only thing you should use Acrobat for is creating PDFs, and viewing protected documents. Otherwise, make sure your PDFs open by default in Preview using the Get Info box in the Finder. Do not use the Acrobat plugin. It should be disabled or removed (or use TenFourFox, natch, which won't even run it).

Microsoft Virtual PC (and other PC emulators): I won't belabour this point except to say this depends greatly on what you run inside the emulator. Remember that a virtual machine installation of Windows can be just as hosed as a real installation, and can be an even greater malware risk if it has network access. Some Linuces will still run in VPC (I used to use Knoppix). Otherwise, stick to Windows and patch patch patch, and/or completely disable networking or enable bridged mode, which uses your Mac as a firewall for the emulated PC, as appropriate.

* * *

Watch this blog as other security-related posts appear. Yes, your Power Mac has holes, but until such time as they can't be plugged or the system is no longer fit for your purpose, nothing says the only choices are a forced upgrade or sit unprotected. So far we've made our systems last over a decade. I think we can still safely keep them viable a while longer.

5 comments:

  1. Doesn't enabling the firewall technically increase the attack surface?

    ReplyDelete
    Replies
    1. In the sense that it runs a new layer, yes, theoretically, but by filtering port access it would reduce other kinds of inadvertent holes. The firewall used in 10.6 and earlier is ipfw, which has an excellent security reputation (in 10.4 and up at least, it's ipfw2, see https://opensource.apple.com/source/network_cmds/network_cmds-245.19/ipfw.tproj/ipfw2.c.auto.html ).

      Delete
  2. When you first mentioned the NTP exploit a while back, I disabled the automatic time-updater and noticed pretty quickly that my clock would go off in a few days (enough to cause certificates to fail), so I wrote a simple 'Stay-Open' Applescript bundle that triggers /usr/sbin/ntpdate -u via shell script every 60 minutes and all been accurate for years now! I do have to change the embeded password each time I change my user password, but If anyone's interested, I can post the apple-script here.

    ReplyDelete
  3. Any way to get NBC Nightly News content to play in TenFourFox? G4 iMac, 7450.

    https://www.nbcnews.com/nightly-news

    ReplyDelete
    Replies
    1. I wrote this a while back and just checked it and it pulls them right up!
      http://ppcluddite.blogspot.com/2016/06/new-ppc-media-center-version-6.html

      BTW a new version is coming soon with some stability fixes. Keep on eye on PPCLuddite from more info.

      Delete

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