Update docs/source/format/Security.rst

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: pitrou

docs/source/format/Security.rst

@@ -39,14 +39,18 @@ process' address space. As such, in-memory Arrow data should be accessed with ca
 Invalid data
 ------------
 
-Reading and interpreting Arrow data involves reading into several buffers,
+Arrow is a low level memory format, and the contents of Arrow
+buffers are often combined and treated as pointers into the process 
+memory space. Invalid Arrow data may cause invalid memory accesses
+(potentially crashing the process) or permit access to non-Arrow data
+(potentially allowing an attacker to exfiltrate confidential information).
+
+For example, reading and interpreting Arrow data involves reading into several buffers,
 sometimes in non-trivial ways. This may for instance involve data-dependent
 indirect addressing: to read a value from a Binary array, you need to
 1) read its offsets in buffer #2, and 2) read the range of bytes delimited by
 these offsets in buffer #3. If the offsets are invalid (deliberately or not),
-then step 2) can access invalid memory (potentially crashing the process) or
-memory unrelated to Arrow (potentially allowing an attacker to exfiltrate
-confidential data).
+then step 2) can access invalid memory.
 
 .. TODO:
    For each layout, we should list the associated security risks and the recommended