Security advisory: Recently reported zlib compression issue impacts Qt

zlib has recently reported that it has a security issue when deflating which could cause memory corruption if the input has many distant matches. This is reported in a bit more detail here: https://github.com/madler/zlib/issues/605 and has been assigned the CVE id CVE-2018-25032. This has been fixed in an update to zlib 1.2.12

This affects some aspects of Qt, particularly when compressing ODF files (via QTextDocumentWriter), compressing PNG files when they are saved and also when qCompress() is used.

Solution: Apply the following patch or update to Qt 5.15.9, Qt 6.2.5, or Qt 6.3.0.

Patches:

dev: https://codereview.qt-project.org/c/qt/qtbase/+/403020
6.3: https://codereview.qt-project.org/c/qt/qtbase/+/403623 or https://download.qt.io/official_releases/qt/6.3/CVE-2018-25032-qtbase-6.3.diff
6.2: https://codereview.qt-project.org/c/qt/qtbase/+/403625  or https://download.qt.io/official_releases/qt/6.2/CVE-2018-25032-qtbase-6.2.diff
5.15: https://codereview.qt-project.org/c/qt/tqtc-qtbase/+/403628 or https://download.qt.io/official_releases/qt/5.15/CVE-2018-25032-qtbase-5.15.diff