Subject: [ASA-202004-13] git: information disclosure

Arch Linux Security Advisory ASA-202004-13
==========================================

Severity: High
Date    : 2020-04-14
CVE-ID  : CVE-2020-5260
Package : git
Type    : information disclosure
Remote  : Yes
Link    : https://security.archlinux.org/AVG-1133

Summary
=======

The package git before version 2.26.1-1 is vulnerable to information
disclosure.

Resolution
==========

Upgrade to 2.26.1-1.

# pacman -Syu "git>=2.26.1-1"

The problem has been fixed upstream in version 2.26.1.

Workaround
==========

The most complete workaround is to disable credential helpers
altogether:

  git config --unset credential.helper
  git config --global --unset credential.helper
  git config --system --unset credential.helper

An alternative is to avoid malicious URLs:
1. Examine the hostname and username portion of URLs fed to git clone
for the presence of encoded newlines (%0a) or evidence of credential-
protocol injections (e.g., host=github.com)
2. Avoid using submodules with untrusted repositories (don't use clone
--recurse-submodules; use git submodule update only after examining the
URLs found in .gitmodules)
3. Avoid tools which may run git clone on untrusted URLs under the hood

Description
===========

Affected versions of Git have a vulnerability whereby Git can be
tricked into sending private credentials to a host controlled by an
attacker. Git uses external "credential helper" programs to store and
retrieve passwords or other credentials from secure storage provided by
the operating system. Specially-crafted URLs that contain an encoded
newline can inject unintended values into the credential helper
protocol stream, causing the credential helper to retrieve the password
for one server (e.g., good.example.com) for an HTTP request being made
to another server (e.g., evil.example.com), resulting in credentials
for the former being sent to the latter. There are no restrictions on
the relationship between the two, meaning that an attacker can craft a
URL that will present stored credentials for any host to a host of
their choosing.
The vulnerability can be triggered by feeding a malicious URL to git
clone. However, the affected URLs look rather suspicious; the likely
vector would be through systems which automatically clone URLs not
visible to the user, such as Git submodules, or package systems built
around Git. The problem has been patched in the versions published on
April 14th, 2020, going back to v2.17.x. Anyone wishing to backport the
change further can do so by applying commit 9a6bbee (the full release
includes extra checks for git fsck, but that commit is sufficient to
protect clients against the vulnerability). The patched versions are:
2.17.4, 2.18.3, 2.19.4, 2.20.3, 2.21.2, 2.22.3, 2.23.2, 2.24.2, 2.25.3,
2.26.1.

Impact
======

A remote attacker could trick Git into returning credential information
for a wrong host by providing a malicious URL.

References
==========

https://github.com/git/git/security/advisories/GHSA-qm7j-c969-7j4q
https://lore.kernel.org/git/xmqqy2qy7xn8.fsf@gitster.c.googlers.com/
https://git.kernel.org/pub/scm/git/git.git/commit/?id=9a6bbee8006c24b46a85d29e7b38cfa79e9ab21b
https://git.kernel.org/pub/scm/git/git.git/commit/?id=c716fe4bd917e013bf376a678b3a924447777b2d
https://git.kernel.org/pub/scm/git/git.git/commit/?id=07259e74ec1237c836874342c65650bdee8a3993
https://bugs.chromium.org/p/project-zero/issues/detail?id=2021
https://security.archlinux.org/CVE-2020-5260