> For the complete documentation index, see [llms.txt](https://reports.immunefi.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://reports.immunefi.com/fuel-network-or-attackathon/attackathon-_-fuel-network-33303-smart-contract-medium-incorrect-sign-change.md). # Attackathon \_ Fuel Network 33303 - \[Smart Contract - Medium] Incorrect sign change Submitted on Wed Jul 17 2024 10:37:38 GMT-0400 (Atlantic Standard Time) by @shadowHunter for [Attackathon | Fuel Network](https://immunefi.com/bounty/fuel-network-attackathon/) Report ID: #33303 Report type: Smart Contract Report severity: Medium Target: Impacts: * Compiler bug ## Description This is a compiler bug since resulting value 0 sign is changed to negative. This library are meant to be used by third party apps as mentioned by Fuel team in github page ## Brief/Intro It seems that if you are adding same number with different sign then resulting 0 sign is changed which is not correct ## Vulnerability Details 1. If `add` is called using number 3 and -3 then result should be 0 with positive sign 2. But since 3>3 is false so condition move to else condition which changes the sign even though it was not required ``` if self.underlying > other.underlying { underlying = self.underlying - other.underlying; } else { underlying = other.underlying - self.underlying; non_negative = false; } ``` 4. Ideally the condition should be `if self.underlying >= other.underlying` ## Impact Details Result will be with incorrect sign ## References ## Proof of concept ## Proof of Concept ``` script; use sway_libs::fixed_point::ifp64::IFP64; use std::assert::assert; fn main() -> bool { let num = IFP64::from_uint(42_u32); let num2 = IFP64::from_uint(42_u32); let mut res = num + num2.sign_reverse(); // fails since resulting 0 has -ve sign assert(res.non_negative()); true } ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://reports.immunefi.com/fuel-network-or-attackathon/attackathon-_-fuel-network-33303-smart-contract-medium-incorrect-sign-change.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.