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Date: Mon, 4 Jul 2022 16:17:17 -0400
From: Demi Marie Obenour <>
To: Open Source Software Security <>
Subject: Re: Denial of service in GnuPG

It has come to my attention that my original post caused at least two
mail clients to hang.  Sorry about that; I did not expect any mail
client to eagerly parse the attachments.  This version wraps the
attachments in a password-protected zip file (password: MitB7vqh).  It
also includes some additional information.

GnuPG is vulnerable to a denial of service attack when processing
crafted detached signatures and/or certificates.  By concatenating the
same signature to itself a very large number of times, and then wrapping
them in a compressed packet, I am able to cause GnuPG to take over a
minute to process an input that is less than 5KB armored.

I have attached two files:

- A patch (based on one submitted upstream) that fixes the bug for keys,
  detached signatures, and cleartext signatures.  It does not fix the
  bug for other types of OpenPGP data, as I am not sure if the obvious
  fix (only allowing a single literal data packet in a compressed
  packet) would render data already in the wild inaccessible.  The only
  difference between this patch and the one sent upstream already is that
  this one prevents attacks involving cleartext signatures.

- An encrypted zip file (see above for password) that contains a proof
  of concept exploit.  Both the public key and the detached signature
  (of an empty file) are included.
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

View attachment "v3-0001-Disallow-compressed-signatures-and-certificates.patch" of type "text/plain" (8134 bytes)

Download attachment "" of type "application/zip" (4070 bytes)

Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)

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