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EUVD-2026-275981

2026-10-05T21:08:11.633837+00:00

EUVD-2026-275981

fkie_cve-2026-32129

2026-10-05T21:08:11.633877+00:00

soroban-poseidon provides Poseidon and Poseidon2 cryptographic hash functions for Soroban smart contracts. Poseidon V1 (PoseidonSponge) accepts variable-length inputs without injective padding. When a caller provides fewer inputs than the sponge rate (inputs.len() < T - 1), unused rate positions are implicitly zero-filled. This allows trivial hash collisions: for any input vector [m1, ..., mk] hashed with a sponge of rate > k, hash([m1, ..., mk]) equals hash([m1, ..., mk, 0]) because both produce identical pre-permutation states. This affects any use of PoseidonSponge or poseidon_hash where the number of inputs is less than T - 1 (e.g., hashing 1 input with T=3). Poseidon2 (Poseidon2Sponge) is not affected.

GHSA-g2p6-hh5v-7hfm — Poseidon V1 variable-length input collision via implicit zero-padding

2026-10-05T21:08:11.633916+00:00

Affected: crates.io: soroban-poseidon

## Impact

Poseidon V1 (`PoseidonSponge`) accepts variable-length inputs without injective padding. When a caller provides fewer inputs than the sponge rate (`inputs.len() < T - 1`), unused rate positions are implicitly zero-filled. This allows trivial hash collisions: for any input vector `[m1, ..., mk]` hashed with a sponge of rate > k, `hash([m1, ..., mk])` equals `hash([m1, ..., mk, 0])` because both produce identical pre-permutation states.

This affects any use of `PoseidonSponge` or `poseidon_hash` where the number of inputs is less than `T - 1` (e.g., hashing 1 input with `T=3`).

Poseidon2 (`Poseidon2Sponge`) is **not affected** — it encodes the input length in the capacity element (`IV = input_len << 64`), making different-length inputs produce distinct states.

## Patches

Fixed by enforcing `inputs.len() == RATE` in `PoseidonSponge::compute_hash`, matching circom's invariant that `nInputs` always equals `T - 1`. Users should upgrade to the next release containing this fix.

## Workarounds

If upgrading is not immediately possible:

- Ensure callers **always** use `T = inputs.len() + 1` (full-rate), which is how circom uses Poseidon. For example, to hash 2 inputs, use `T=3`; to hash 1 input, use `T=2`. Never use a sponge with more rate capacity than the number of inputs. - Alternatively, migrate to `Poseidon2Sponge`, which is safe for variable-length inputs due to its length-encoding IV.

## References - [circom Poseidon implementation](https://github.com/iden3/ci…