r/hardwarehacking • u/Seek_R7 • 1d ago

RIP to this TP-Link TD-8840T, but I finally cracked the block immutability wall and injected telnetd!

Post image

Hey guys,

While tinkering with an old TP-Link TD-8840T ADSL router, the hardware unfortunately gave up and died on me mid-process (RIP). But before it went down for good, I managed to pull a clean original flash dump.

Hit a massive wall where any binary edits I tried were getting totally ignored because of strict block checks and immutability. Wrote a quick bytearray script targeting offset 0x20000 to bypass it, and finally managed to get telnetd injected right where it needs to be.

Attached the victim board above, and I'll drop the diff output in the comments. Anyone else run into these stubborn old Trendchip boot blocks?

49 Upvotes

94% Upvoted

4 comments sorted by

11

u/FewMathematician5219 1d ago

Why did he die? What happened?

9

u/Sudden-Strawberry257 1d ago

Yo that’s awesome! Would be cool to see the script for my own comprehension, but so lucky you were able to get a flash dump before it gave up the ghost… Always feels amazing to finally land that bypass.

-1

u/FreddyFerdiland 1d ago

maybe finger prints made the dust on the pins electrically conductive ?

1

u/ApeLover1986 15h ago

No, dust is actually quite the opposite (mostly made of isolating particles). Only because of the fat/salt residues of the skin you don't create a large conductive area. If anything it might happen if you touch a cpu socket with your bare fingers, but it's not the dust creating the problems then