ttf-mscorefonts-installer drop-priv warnings and download errors during install

Status changed to 'Confirmed' because the bug affects multiple users.

Not exactly the same error message as in widely-impacting bug 1607535, but almost, and judging by the attachments to your bug report, your version of package apt-transport-https is < 1.2.19. Please update this package (and other apt packages, for good measure) to 1.2.19, and retry (reinstall ttf-mscorefonts-installer). Chances are it's the same bug, fixed in apt-transport-https 1.2.19.

Affects me with apt-transport-htts version 1.3.4:

> apt show apt-transport-https

Package: apt-transport-https
Version: 1.3.4
Priority: standard
Section: admin
Source: apt
Origin: Ubuntu
Maintainer: Ubuntu Developers <email address hidden>
Original-Maintainer: APT Development Team <email address hidden>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 241 kB
Depends: libapt-pkg5.0 (>= 1.3~rc2), libc6 (>= 2.14), libcurl3-gnutls (>= 7.16.2), libgcc1 (>= 1:3.0), libstdc++6 (>= 5.2)
Recommends: ca-certificates
Task: standard
Phased-Update-Percentage: 40
Supported: 9m
Download-Size: 34,3 kB
APT-Manual-Installed: yes
APT-Sources: http://ua.archive.ubuntu.com/ubuntu yakkety-updates/main amd64 Packages
Description: https download transport for APT
 This package enables the usage of 'deb https://foo distro main' lines
 in the /etc/apt/sources.list so that all package managers using the
 libapt-pkg library can access metadata and packages available in sources
 accessible over https (Hypertext Transfer Protocol Secure).
 .
 This transport supports server as well as client authentication
 with certificates.

On Yakkety? That's weird. What error message does "sudo apt-get install --reinstall ttf-mscorefonts-installer" return, precisely?

Although the request was for Yakketty, it also has the the bug in Xenial. I did try to manually download arial32.exe and andale32.exe using wget and then copying them to /var/lib/update-notifier/package-data-downloads/partial. Doing so allowed the reconfigure to succeed.

sudo apt show apt-transport-https
[sudo] password for admin0:
Package: apt-transport-https
Version: 1.2.19
Priority: standard
Section: admin
Source: apt
Origin: Ubuntu
Maintainer: Ubuntu Developers <email address hidden>
Original-Maintainer: APT Development Team <email address hidden>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 213 kB
Depends: libapt-pkg5.0 (>= 1.1~exp15), libc6 (>= 2.14), libcurl3-gnutls (>= 7.16.2), libgcc1 (>= 1:3.0), libstdc++6 (>= 5.2)
Recommends: ca-certificates
Task: standard
Supported: 5y
Download-Size: 26.0 kB
APT-Manual-Installed: yes
APT-Sources: http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
Description: https download transport for APT
 This package enables the usage of 'deb https://foo distro main' lines
 in the /etc/apt/sources.list so that all package managers using the
 libapt-pkg library can access metadata and packages available in sources
 accessible over https (Hypertext Transfer Protocol Secure).
 .
 This transport supports server as well as client authentication
 with certificates.

[Before file downloads]
sudo apt-get install --reinstall ttf-mscorefonts-installer
[sudo] password for admin0:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-headers-4.4.0-64 linux-headers-4.4.0-64-generic
  linux-image-4.4.0-64-generic linux-image-extra-4.4.0-64-generic
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 2 not upgraded.
Need to get 29.5 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://us.archive.ubuntu.com/ubuntu xenial/multiverse amd64 ttf-mscorefonts-installer all 3.4+nmu1ubuntu2 [29.5 kB]
Fetched 29.5 kB in 0s (84.9 kB/s)
Preconfiguring packages ...
(Reading database ... 421788 files and directories currently installed.)
Preparing to unpack .../ttf-mscorefonts-installer_3.4+nmu1ubuntu2_all.deb ...
mscorefonts-eula license has already been accepted
Unpacking ttf-mscorefonts-installer (3.4+nmu1ubuntu2) over (3.4+nmu1ubuntu2) ...
Processing triggers for fontconfig (2.11.94-0ubuntu1.1) ...
Processing triggers for update-notifier-common (3.168.3) ...
ttf-mscorefonts-installer: processing...
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/andale32.exe
Get:1 http://downloads.sourceforge.net/corefonts/andale32.exe [198 kB]
Fetched 198 kB in 7s (27.2 kB/s)
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/andale32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/arial32.exe
Err:1 http...

@Patrick: I was asking Timofey, who reports being affected by this bug with apt-transport-https 1.3.4 on Yakkety. That shouldn't be the case, and any error that makes it look like it is can be solved away by removing the partially-downloaded fonts in /var/lib/update-notifier/package-data-downloads/partial/ and reinstalling ttf-mscorefonts-installer after updating apt-transport-https to 1.3.4 (Yakkety) or 1.2.19 (Xenial). Cf. bug 1607535's description, section [Fix].