Rust 1.91.0 Not Recommended

[leighmcculloch]

The Rust Release Team has posted on their blog that Rust 1.91.0 contains a bug with building wasm that could cause undefined behaviour, with a fix in Rust 1.91.1. For more details see the post below.

https://blog.rust-lang.org/2025/11/10/Rust-1.91.1/

[anupsdf]

After doing an internal review, SDF concluded that Soroban contracts are probably not impacted by this issue. Soroban contracts can only import functions from the Soroban host, not from external crates. Therefore they are not impacted by this mangling bug. However, to be extra cautious SDF has released stellar-cli v23.2.0 which blocks compiling contracts using Rust v1.91.0.

If any contract developer wishes to verify this on their own they could follow these steps to see if there is any impact to their contracts:
Step 1. Have the wasm that was uploaded on-chain if compiled by rust 1.91.0
Step 2. Recompile the contract using rust v1.91.1
Step 3. Use wasm-objdump utility to deconstruct the two wasms above and inspect the "Import section" to see if there are any differences.

Here is a sample output from wasm-objdump showing the Import section, https://github.com/anupsdf/stellar-contract-wasms/blob/main/wasm_analysis/2ae525f01dc69d900c3faac9276c6a8514e916325a39fdf27228b43341aa114a_objdump.txt#L46-L72