Excel workbook protection and sheet protection are commonly used as if they provide file security. It turns out that these mechanisms do NOT provide file security, nor were they ever intended to do so. Section 18.2.29 of ECMA-376-1:2016, the latest version of the standard governing Office Open XML, says the following:
Applications might use workbook protection to prevent anyone from accidentally changing, moving, or deleting important data. This protection can be ignored by applications which choose not to support this optional protection mechanism.
The same section contains an additional note:
Worksheet or workbook element protection should not be confused with file security. It is not meant to make your workbook safe from unintentional modification, and cannot protect it from malicious modification.
Both sheet protection and workbook protection may be removed without the protection password in four basic steps:
I have published a detailed PDF guide for accomplishing these steps using only File Explorer and Notepad on Windows.
Is anyone else surprised by how easy it is to bypass these protections?
(Score: 0) by Anonymous Coward on Monday July 08 2019, @06:41PM
Not the GP, but that is technically only making it "harder" to edit. Beside the obvious of just retyping it into a new version, you could, theoretically, tamper with the message and still have a good signature. Different algorithms have different sensitivity to this, of course, but it is a distinct possibility, even more so if you don't use an iterative hash or something like MD5 or SHA-512, which are vulnerable to length extension attacks.