Worked example · 2022-03

Agave / Hundred Finance reentrancy exploit — Gnosis Chain — 2022-03-15

Loss

Agave lost 2,116 ETH (about $5.5M) and Hundred Finance 2,363 ETH (about $6.2M), about $11.7M in total [rektagave]; The Block rounds the total to about $11M [theblockagave]. This file covers Agave; Hundred Finance was hit by the same root cause minutes later.

OAK Techniques observed

OAK-T9.005 (Reentrancy — primary; the attacker re-entered borrow logic through a post-transfer hook on Gnosis Chain tokens, borrowing more than the protocol recorded as debt [rektagave]). OAK-T1.007 (Token-2022 Transfer-Hook Abuse — original cross-standard analogy, retained as the original mapping).

Attribution

unattributed pseudonymous. Rekt lists separate attacker addresses for Agave and Hundred and names no individuals; none of the funds were reported returned, and the proceeds were sent to Tornado Cash [rektagave]. Sources cited here do not establish that the two attacks were by the same actor.

Corrected 2026-10-11

Agave is an Aave fork (not Compound V2) and Hundred Finance is the Compound fork; losses are about $5.5M for Agave (the file said about $5M across both); the "same attacker" claim and unsourced post-mortem/analyst references were removed.

Key teaching point

Lending-market forks deployed on a chain whose tokens run a callback on transfer inherit a reentrancy surface that the original deployment did not have. Sending borrowed tokens before updating the user's debt is the vulnerable ordering [immunefihundred].