Python 2.7.x is vulnerable to a Heap-Buffer-Overflow as well as a Heap-Use-After-Free. The vulnerability lies when multiply threads are handling large amounts of data. In both cases there is essentially a race condition that occurs. For the Heap-Buffer-Overflow, Thread 2 is creating the size for a buffer, but Thread1 is already writing to the buffer without knowing how much to write. So when a large amount of data is being processed, it is very easy to cause memory corruption using a Heap-Buffer-Overflow. As for the Use-After-Free, Thread3->Malloc->Thread1->Free's->Thread2-Re-uses-Free'd Memory.
Created python tracking bugs for this issue:
Affects: fedora-all [bug 1541559]
Versions of Python 2 included in Red Hat Enterprise Linux 6 and 7 are affected by this issue. Reading concurrently from the same file handle in multiple threads is inherently unstable, and should not be relied upon in any real program. This issue is not planned to be fixed in future releases.
This CVE assignment was disputed by upstream. While an attack is theoretically possible, it relies on a programming pattern in the vulnerable Python program that is generally considered bad practice if not an outright bug.