We stopped trusting filenames
Written by The LynxDock Team, Engineering, LynxDock
The simplest way to get something unpleasant into a chat application is to rename it. An executable becomes holiday.png, the interface shows a picture icon, and everything downstream that trusts the extension is now confidently working with a lie.
LynxDock now checks the file instead of the filename. Every attachment is read at the front, and its leading bytes - its signature, or magic number - are compared against the type it claims to be. All eight permitted types carry a real signature check.
Where that check lives matters as much as the check itself. It runs inside the storage call rather than in the interface, so no alternative code path can reach the disk without passing it. If the bytes and the claimed type disagree, the write is refused with a plain error rather than quietly accepted.
The part we would point at in review is not the feature, it is the negative test. We take a genuine image, rename a binary to sit beside it wearing the same extension, and assert that the second one is rejected. A security control without a test proving it says no is a hope, not a control.
This is deliberately narrow. It is not malware scanning and it does not make arbitrary files safe. It removes one specific lie - the claim a filename makes about what it contains - which is the lie this particular door was open to.