Why chmod 777 is dangerous: full permissions explained and safer alternatives
Don't use 777. If you're getting permission denied errors, diagnose the actual problem (wrong owner, wrong group, SELinux context) instead of opening the floodgates. Use 755 for directories, 644 for files, and if a web server needs write access to a specific directory, use 775 with the web server user in the group.
chmod 777 sets permissions to rwxrwxrwx: every user on the system can read, write, and execute the file or directory. It's the nuclear option of file permissions and the most common security mistake made by developers who are frustrated with permission errors and reach for 777 to make the problem go away.
By TechCompare · Updated
How this is calculated
777 gives every user, process, and service read, write, and search or execute permission on the target. For a regular file, changing or deleting its directory entry is controlled mainly by the containing directory, not the file's own write bit. A 777 directory, however, lets users create and remove entries unless the sticky bit is set. On a shared server, another user's compromised WordPress plugin can now deface your site. The only common legitimate case is a shared temporary directory like /tmp with sticky-bit protection. Never leave ordinary application paths at 777 in production.
Verdict
777 sets all three permission classes to 7 (4+2+1, full read+write+execute). On a regular file that permits everyone to write it, but deleting or renaming it still depends on write and search permission on its parent directory. On a 777 directory, those directory permissions allow any user to create, remove, or rename entries unless the sticky bit is set. The reason that's almost always wrong is that a permission error usually points to ownership or group membership, not missing world access. For shared write access, use 775 with a shared group and setgid where appropriate.