Vulnerabilities
Misconfiguration
Runtime Security
Compliance
CVE Vulnerabilities

CVE-2021-21300

Improper Link Resolution Before File Access ('Link Following')

Published: Mar 09, 2021 | Modified: Nov 07, 2023
CVSS 3.x
7.5
HIGH
Source:
NVD
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS 2.x
5.1 MEDIUM
AV:N/AC:H/Au:N/C:P/I:P/A:P
RedHat/V2
RedHat/V3
Ubuntu
Additional information
NVDhttps://nvd.nist.gov/vuln/detail/CVE-2021-21300
CWEhttps://cwe.mitre.org/data/definitions/59.html

Git is an open-source distributed revision control system. In affected versions of Git a specially crafted repository that contains symbolic links as well as files using a clean/smudge filter such as Git LFS, may cause just-checked out script to be executed while cloning onto a case-insensitive file system such as NTFS, HFS+ or APFS (i.e. the default file systems on Windows and macOS). Note that clean/smudge filters have to be configured for that. Git for Windows configures Git LFS by default, and is therefore vulnerable. The problem has been patched in the versions published on Tuesday, March 9th, 2021. As a workaound, if symbolic link support is disabled in Git (e.g. via git config --global core.symlinks false), the described attack wont work. Likewise, if no clean/smudge filters such as Git LFS are configured globally (i.e. before cloning), the attack is foiled. As always, it is best to avoid cloning repositories from untrusted sources. The earliest impacted version is 2.14.2. The fix versions are: 2.30.1, 2.29.3, 2.28.1, 2.27.1, 2.26.3, 2.25.5, 2.24.4, 2.23.4, 2.22.5, 2.21.4, 2.20.5, 2.19.6, 2.18.5, 2.17.62.17.6.

Weakness

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Affected Software

Name Vendor Start Version End Version
Git Git-scm * 2.14.2 (including)
Git Git-scm 2.17.0 (including) 2.17.6 (excluding)
Git Git-scm 2.18.0 (including) 2.18.5 (excluding)
Git Git-scm 2.19.0 (including) 2.19.6 (excluding)
Git Git-scm 2.20.0 (including) 2.20.5 (excluding)
Git Git-scm 2.21.0 (including) 2.21.4 (excluding)
Git Git-scm 2.22.0 (including) 2.22.5 (excluding)
Git Git-scm 2.23.0 (including) 2.23.4 (excluding)
Git Git-scm 2.24.0 (including) 2.24.4 (excluding)
Git Git-scm 2.25.0 (including) 2.25.5 (excluding)
Git Git-scm 2.26.0 (including) 2.26.3 (excluding)
Git Git-scm 2.29.0 (including) 2.29.3 (excluding)
Git Git-scm 2.30.0 (including) 2.30.2 (excluding)
Git Git-scm 2.27.0 (including) 2.27.0 (including)
Git Git-scm 2.28.0 (including) 2.28.0 (including)

Potential Mitigations

  • Follow the principle of least privilege when assigning access rights to entities in a software system.
  • Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

References

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