Printing stopped working in one program, and the font is to blame

Here's an odd one worth knowing about, because the symptom points you at entirely the wrong thing. If some program on your PC has refused to print since the middle of August, or falls over when you ask it to save a PDF, and the printer works fine from everything else, look at the font.

Microsoft has confirmed a bug in the August .NET Framework updates. Certain programs now fail with a System.IO.FileFormatException the moment they try to print or export anything set in Calibri. The full list is Calibri, Cambria, Constantia and Corbel, fifteen individual weights and italics between them. All four ship with Windows and Calibri was Office's default typeface for well over a decade, so an enormous number of documents are set in one of them.

The cause is a piece of very old sloppiness inside the font files themselves. Each one has a spacing table that records its own length in a field too small to hold the real number, so the figure wraps around. Calibri Bold's table is genuinely 160,164 bytes; the file claims 29,088. Nothing ever noticed, because Windows normally ignores that table. The August update added a bounds check that closes two real security holes, and the check now throws out the entire font rather than skipping one bad table. It's KB5120708 on Windows 11 and KB5120709 on Windows 10, both dated 11 August, plus the equivalents for older systems.

Microsoft's official workaround is a configuration change meant for whoever wrote the program, and it switches the new security protection back off, which is not a trade you want on a home PC. The quiet fix is better: set the document, report or template to Arial or Segoe UI and print it. And if you're genuinely unsure whether the trouble is the update or the hardware, Tendvane's printer repair wizard checks the spooler and the queue, which at least tells you which side to blame.