Announcement post: https://mail.python.org/archives/list/security-announce@python.org/thread/C5RIXC2ZIML3NOEIOGFPA6ISGU5L2QXL/

CVE-2020-15523 is an invalid search path in Python 3.6 and later on 
Windows. It occurs during Py_Initialize() when the runtime attempts to 
pre-load python3.dll. If Py_SetPath() has been called, the expected 
location is not set, and locations elsewhere on the user's system will 
be searched.

This issue is not triggered when running python.exe. It only applies 
when CPython has been embedded in another application.

Issue: https://bugs.python.org/issue29778
Patch: https://github.com/python/cpython/pull/21297

The next patched releases will be: 3.9.0b5, 3.8.4, 3.7.9 (source only), 
3.6.12 (source only)

Other than applying the patch, applications may mitigate the 
vulnerability by explicitly calling LoadLibrary() on their copy of 
python3.dll before calling Py_Initialize(). Even with the patch applied, 
applications should include a copy of python3.dll alongside their main 
Python DLL.

Thanks to Eric Gantumur for detecting and reporting the issue to the 
Python Security Response Team.