do_ed_script in pch.c in GNU patch through 2.7.6 does not block strings beginning with a ! character. NOTE: this is the same commit as for CVE-2019-13638 , but the ! syntax is specific to ed, and is unrelated to a shell metacharacter.GNU patch through 2.7.6 is vulnerable to OS shell command injection that can be exploited by opening a crafted patch file that contains an ed style diff payload with shell metacharacters. The ed editor does not need to be present on the vulnerable system. This is different from CVE-2018-1000156 .