id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
35905	Sign (or encrypt) pickle cache traffic to protect against remote code execution through cache takeover	Sebastian Pipping		"Hi!

Multiple of the Django cache backends at `django/core/cache/backends/*.py` seem to make use of pickle:

{{{
# git --no-pager grep -ilF pickle django/core/cache/backends/
django/core/cache/backends/db.py
django/core/cache/backends/filebased.py
django/core/cache/backends/locmem.py
django/core/cache/backends/memcached.py
django/core/cache/backends/redis.py
}}}

From what I can see, none of them sign or encrypt what goes into and out of the cache, despite available tools in `django/core/signing.py`.  For local process memory, that may be alright, and for file system based caches it's probably understood that using a directory that is writable to attackers is trouble anyway.  The most interesting I believe are `memcached.py` and `redis.py` because now if an attacker obtains write access to the instance of memcached or Redis that is used for a Django cache backend, they gain arbitrary code execution in Django.  That's probably known for years (and explained at e.g. https://www.blackduck.com/blog/python-pickling.html or https://davidhamann.de/2020/04/05/exploiting-python-pickle/), yet neither of these two backends have started signing (and validating the signature) or encrypting (and decrypting) the cache traffic yet. There is some performance penalty to be expected but a new boolean cache option `SIGN` could turn its default back from ""sign, validate and be secure"" to ""insecure and faster"" for users that have a threat model where owning the cache was game over already and they sign up for the risk.

Recent case https://github.com/climateconnect/climateconnect/pull/1331#issuecomment-2397881433 is an example of a setup where use of a pickling cache lead to potential remote code execution, which is one reason I'm bringing this up here.

I can help with one or more pull requests on the topic, provided that there is agreement on its importance, its value and general direction.

What do you think?
"	New feature	closed	Core (Cache system)	dev	Normal	wontfix	cache security	Sebastian Pipping	Unreviewed	0	0	0	0	0	0