Organizations that use Git as a code repository are vulnerable to an attack through submodules and should update their code immediately. The vulnerability, described in CVE-2018-17456, can allow arbitrary code to be executed when a user clones a subdirectory containing malicious code.
The vulnerability - an option-injection attack - is described as quite similar to an earlier vulnerability in a GitHub blog post announcing the issue and its solution. That bug, CVE-2017-1000117, previously had been patched.
The option-injection flaw was reported through the GitHub Bug Bounty program on September 23, with a coordinated disclosure date of October 5.
GitHub Desktop, Atom, the CLI version of Git, and applications that might have embedded Git are all affected by the vulnerability. GitHub Enterprise and GitHub.com are not vulnerable to this flaw, however.