Firefox 111 patches 11 holes, but not 1 zero-day among them…


Heard of cricket (the sport, not the insect)?

It’s much like baseball, except that batters can hit the ball wherever they like, including backwards or sideways; bowlers can hit the batter with the ball on purpose (within certain safety limits, of course – it just wouldn’t be cricket otherwise) without kicking off a 20-minute all-in brawl; there’s almost always a break in the middle of the afternoon for tea and cake; and you can score six runs at a time as long as you hit the ball high and far enough (seven if the bowler makes a mistake as well).

Well, as cricket enthusiasts know, 111 runs is a superstitious score, considered inauspicious by many – the cricketer’s equivalent of Macbeth to an actor.

It’s known as a Nelson, though nobody actually seems to know why.

Today therefore sees Firefox’s Nelson release, with version 111.0 coming out, but there doesn’t seem to be anything inauspicious about this one.

Eleven individual patches, and two batches-of-patches

As usual, there are numerous security patches in the update, including Mozilla’s usual combo-CVE vulnerability numbers for potentially exploitable bugs that were found automatically and patched without waiting to see if a proof-of-concept (PoC) exploit was possible:

  • CVE-2023-28176: Memory safety bugs fixed in Firefox 111 and Firefox ESR 102.9. These bugs were shared between the current version (which includes new features) and the ESR version, short for extended support release (security fixes applied, but with new features frozen since version 102, nine releases ago).
  • CVE-2023-28177: Memory safety bugs fixed in Firefox 111 only. These bugs almost certainly only exist in new code that brought in new features, given that they didn’t show up in the older ESR codebase.

These bags-of-bugs have been rated High rather than Critical.

Mozilla admits that “we presume that with enough effort some of these could have been exploited to run arbitrary code”, but no one has yet figured out how to do so, or even if such exploits are feasible.

None of the other eleven CVE-numbered bugs this month were worse thah High; three of them apply to Firefox for Android only; and no one has yet (so far as we yet know) come up with a PoC exploit that shows how to abuse them in real life.

Two notably interesting vulnerabilities appear amongst the 11, namely:

  • CVE-2023-28161: One-time permissions granted to a local file were extended to other local files loaded in the same tab. With this bug, if you opened a local file (such as downloaded HTML content) that wanted access, say, to your webcam, then any other local file you opened afterwards would magically inherit that access permission without asking you. As Mozilla noted, this could lead to trouble if you were looking through a collection of items in your download directory – the access permission warnings you’d see would depend on the order in which you opened the files.
  • CVE-2023-28163: Windows Save As dialog resolved environment variables. This is another keen reminder to sanitise thine inputs, as we like to say. In Windows commands, some character sequences are treated specially, such as %USERNAME%, which gets converted to the name of the currently logged-on user, or %PUBLIC%, which denotes a shared directory, usually in C:Users. A sneaky website could use this as a way to trick you into seeing and approving the download of a filename that looks harmless but lands in a directory you wouldn’t expect (and where you might not later realise it had ended up).

What to do?

Most Firefox users will get the update automatically, typically after a random delay to stop everyone’s computer downloading at the same moment…

…but you can avoid the wait by manually using Help > About (or Firefox > About Firefox on a Mac) on a laptop, or by forcing an App Store or Google Play update on a mobile device.

(If you’re a Linux user and Firefox is supplied by the maker of your distro, do a system update to check for the availability of the new version.)

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