CVE-2021-39159

remote code execution via git repo provider

from binderhub.repoproviders import (GitHubRepoProvider,
                            GitLabRepoProvider, GistRepoProvider,
                            ZenodoProvider, FigshareProvider, HydroshareProvider,
                            DataverseProvider)

c.BinderHub.repo_providers =  {
            'gh': GitHubRepoProvider,
            'gist': GistRepoProvider,
            'gl': GitLabRepoProvider,
            'zenodo': ZenodoProvider,
            'figshare': FigshareProvider,
            'hydroshare': HydroshareProvider,
            'dataverse': DataverseProvider,
        }

A remote code execution vulnerability has been identified in BinderHub, where providing BinderHub with maliciously crafted input could execute code in the BinderHub context, with the potential to egress credentials of the BinderHub deployment, including JupyterHub API tokens, kubernetes service accounts, and docker registry credentials. This may provide the ability to manipulate images and other user created pods in the deployment, with the potential to escalate to the host depending on the underlying kubernetes configuration.

Untrusted input reaches a shell command, allowing arbitrary commands to run on the host. Typical impact: code execution in the application's environment.

CVE-2021-39159 has a CVSS score of 9.6 (Critical). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.2.0); upgrading removes the vulnerable code path.

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Patch below, or on GitHub

From 9f4043d9dddc1174920e687773f27b7933f48ab6 Mon Sep 17 00:00:00 2001
From: Riccardo Castellotti <[email protected]>
Date: Thu, 19 Aug 2021 15:49:43 +0200
Subject: [PATCH] Explicitly separate git-ls-remote options from positional
 arguments

---
 binderhub/repoproviders.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/binderhub/repoproviders.py b/binderhub/repoproviders.py
index f33347b..5d4b87c 100755
--- a/binderhub/repoproviders.py
+++ b/binderhub/repoproviders.py
@@ -484,7 +484,7 @@ class GitRepoProvider(RepoProvider):
             self.sha1_validate(self.unresolved_ref)
         except ValueError:
             # The ref is a head/tag and we resolve it using `git ls-remote`
-            command = ["git", "ls-remote", self.repo, self.unresolved_ref]
+            command = ["git", "ls-remote", "--", self.repo, self.unresolved_ref]
             result = subprocess.run(command, universal_newlines=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
             if result.returncode:
                 raise RuntimeError("Unable to run git ls-remote to get the `resolved_ref`: {}".format(result.stderr))
-- 
2.25.1

1. What is CVE-2021-39159? CVE-2021-39159 is a critical-severity OS command injection vulnerability in binderhub (pip), affecting versions < 0.2.0. It is fixed in 0.2.0. Untrusted input reaches a shell command, allowing arbitrary commands to run on the host.
2. How severe is CVE-2021-39159? CVE-2021-39159 has a CVSS score of 9.6 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of binderhub are affected by CVE-2021-39159? binderhub (pip) versions < 0.2.0 is affected.
4. Is there a fix for CVE-2021-39159? Yes. CVE-2021-39159 is fixed in 0.2.0. Upgrade to this version or later.
5. Is CVE-2021-39159 exploitable, and should I be worried? Whether CVE-2021-39159 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-39159 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-39159? Upgrade binderhub to 0.2.0 or later.