CVE-2026-32129 Poseidon V1 variable-length input collision via implicit zero-padding
Attackers can create trivial hash collisions in Poseidon V1 due to implicit zero-padding, compromising integrity for smart contract developers using this library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-32129?
CVE-2026-32129 is a high-severity vulnerability in stellar rs-soroban-poseidon, published on 12 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-328
Which versions are affected by CVE-2026-32129?
2 open source packages ship an affected version, including soroban-poseidon.
| Package | Affected | Fixed in |
|---|---|---|
soroban-poseidon crates.io | All versions | 25.0.1 |
soroban-poseidon crates.io | All versions | 25.0.1 |
How do I fix CVE-2026-32129?
Upgrade soroban-poseidon to 25.0.1 or later.
Is CVE-2026-32129 being exploited?
There is no known exploitation of CVE-2026-32129 in the wild and no public exploit code.
Sources
Also known as GHSA-g2p6-hh5v-7hfm.