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Message-ID: <20260130210336.rbloiah3sbpel5zv@jwilk.net>
Date: Fri, 30 Jan 2026 22:03:36 +0100
From: Jakub Wilk <jwilk@...lk.net>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2025-56005 Undocumented RCE in PLY via
`picklefile` Parameter
TL;DR: CVE-2025-56005 is a nothingburger.
* Alan Coopersmith <alan.coopersmith@...cle.com>, 2026-01-23 11:06:
>https://github.com/bohmiiidd/Undocumented-RCE-in-PLY claims:
>
>>Undocumented Remote Code Execution in PLY CVE-2025-56005
Calling this "remote" is nonsense. Such sensationalism makes me doubt
this advisory was written in good faith.
>>The `picklefile` parameter causes PLY to deserialize a `.pkl` file
>>using Python’s `pickle.load()` **without validation**.
The content of the pickle influences how the input is parsed, so if an
attacker had control over that, it would be a vulnerability in the
program using PLY, regardless of how safe the deserialization is.
I don't see unconstrained unpickling as a vulnerability in PLY; it's
just a missing hardening opportunity.
>>This parameter is *not documented* in the official PLY documentation
>>or GitHub repository,
It's documented in the CHANGES file:
>Added a new picklefile option to yacc() to write the parsing tables to
>a filename using the pickle module. Here is how it works:
>
> yacc(picklefile="parsetab.p")
>
>This option can be used if the normal parsetab.py file is extremely
>large. For example, on jython, it is impossible to read parsing tables
>if the parsetab.py exceeds a certain threshold.
>
>The filename supplied to the picklefile option is opened relative to
>the current working directory of the Python interpreter. If you need to
>refer to the file elsewhere, you will need to supply an absolute or
>relative path.
(How come we're worried about backdoors in the pickle, but not in
parsetab.py?)
OK, I do see a weakness in the API here: Putting the pickle in cwd (as
the example hints) is a bad idea, and some people might be tempted to
put them in /tmp, which is much worse. In contrast, parsetab.py is
written into the same directory as the parser module, which is fine.
PS: I was curious if there's any real-world software that makes use of
this parameter, but to my surprise I found one! Well, not really:
https://github.com/mozilla-firefox/firefox/commit/2a95ef8f868f00e6
self.parser = yacc.yacc(module=self,
outputdir=outputdir,
tabmodule='webidlyacc',
errorlog=yacc.NullLogger()
# Pickling the grammar is a speedup in
# some cases (older Python?) but a
# significant slowdown in others.
# We're not pickling for now, until it
# becomes a speedup again.
# , picklefile='WebIDLGrammar.pkl'
)
--
Jakub Wilk
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