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bug#28618: Emacs Security Issue

From: Dor Azouri
Subject: bug#28618: Emacs Security Issue
Date: Fri, 29 Sep 2017 12:57:06 +0000


This is the output in my env that demonstrates how it works (forgive the hebrew chars):
~/.emacs.d$ ls -all
total 20
drwx------   2 duke duke  4096 ספט 28 20:24 .
drwxr----- 105 duke duke 16384 ספט 28 14:36 ..
~/.emacs.d$ echo '(let ((default-directory "/opt/")) (shell-command "touch stub.file"))' > init.el
~/.emacs.d$ ls -all /opt/ | grep stub.file
~/.emacs.d$ sudo emacs
~/.emacs.d$ ls -all /opt/ | grep stub.file
-rw-r--r--  1 root   root      0 ספט 28 20:25 stub.file
~/.emacs.d$ rm /opt/stub.file 
rm: remove write-protected regular empty file ‘/opt/stub.file’? yes
rm: cannot remove ‘/opt/stub.file’: Permission denied
~/.emacs.d$ sudo rm /opt/stub.file 
~/.emacs.d$ ls -all /opt/ | grep stub.file
address@hidden:~/.emacs.d$ sudo ls -all /root/.emacs
ls: cannot access /root/.emacs: No such file or directory

My env:
GNU Emacs 25.3.2 (tested with old version 23 as well)
Ubuntu 14.04, Kernel 4.13.0

Tested and works as well on Ubuntu 16.04 with emacs24.

Dor Azouri

On Thu, Sep 28, 2017 at 2:25 PM Noam Postavsky <address@hidden> wrote:
tags 28618 + unreproducible

Dor Azouri <address@hidden> writes:

> Reproduction steps:
> ===================
> 1)  Add the following ELisp line of code to the init file. It will be
> loaded on startup and execute the command “touch /stub.file”, when “~
> /.emacs.d/” is the working directory.
>         (let ((default-directory "~/.emacs.d/")) (shell-command
> "touch /stub.file"))
> 2)  Wait for the user to invoke Emacs in elevated mode. The owner of
> the newly created stub file is root.

As Glenn noted, this doesn't actually work: 'sudo emacs' uses
/root/.emacs, not ~/.emacs.

~$ sudo id
uid=0(root) gid=0(root) groups=0(root)
~$ echo '(let ((default-directory "~/.emacs.d/")) (shell-command "touch /stub.file"))' > .emacs
~$ emacs # *Messages* has "touch: cannot touch '/stub.file': Permission denied"
~$ ls /stub.file
ls: cannot access '/stub.file': No such file or directory
~$ sudo emacs
~$ ls /stub.file
ls: cannot access '/stub.file': No such file or directory

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