> 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-33302-smart-contract-medium-exp-function-does-not-work-correctly.md). # Attackathon \_ Fuel Network 33302 - \[Smart Contract - Medium] Exp function does not work correctly Submitted on Wed Jul 17 2024 10:20:43 GMT-0400 (Atlantic Standard Time) by @shadowHunter for [Attackathon | Fuel Network](https://immunefi.com/bounty/fuel-network-attackathon/) Report ID: #33302 Report type: Smart Contract Report severity: Medium Target: Impacts: * Griefing (e.g. no profit motive for an attacker, but damage to the users or the protocol) * Compiler bug ## Description ## Brief/Intro It seems like `exp` function will always return `UFP128::from((1, 0))` no matter what argument is passed. This happens due to mistake in the return variable ```diff -- let res = one; ++ let res = one + _res_minus_1; ``` ## Vulnerability Details 1. Observe the `exp` function ``` impl Exponent for UFP128 { fn exp(exponent: Self) -> Self { let one = UFP128::from((1, 0)); let p2 = one / UFP128::from((2, 0)); let p3 = one / UFP128::from((6, 0)); let p4 = one / UFP128::from((24, 0)); let p5 = one / UFP128::from((120, 0)); let p6 = one / UFP128::from((720, 0)); let p7 = one / UFP128::from((5040, 0)); // common technique to counter losing sugnifucant numbers in usual approximation let _res_minus_1 = exponent + exponent * exponent * (p2 + exponent * (p3 + exponent * (p4 + exponent * (p5 + exponent * (p6 + exponent * p7))))); let res = one; res } } ``` 2. Observe that res is simply returning `one` instead of `one + _res_minus_1` which will be correct exp ## Impact Details Dapp relying on sway library will find itself with incorrect computation of exp. If the resulting was financial calculation then this will cause fund loss to the dapp user ## References ## Proof of concept ## Proof of Concept ``` fn foo() { let mut one = UFP128::from((1, 0)); let two = UFP128::from((2, 0)); res = UFP128::exp(two); assert(res != one); } ``` --- # 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-33302-smart-contract-medium-exp-function-does-not-work-correctly.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.