{"id":"CVE-2026-32129","aliases":["GHSA-g2p6-hh5v-7hfm"],"url":"https://o3.security/vulnerability/CVE-2026-32129","summary":"Poseidon V1 variable-length input collision via implicit zero-padding","details":"## Impact\n\nPoseidon 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.\n\nThis 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`).\n\nPoseidon2 (`Poseidon2Sponge`) is **not affected** — it encodes the input length in the capacity element (`IV = input_len << 64`), making different-length inputs produce distinct states.\n\n## Patches\n\nFixed 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.\n\n## Workarounds\n\nIf upgrading is not immediately possible:\n\n- 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.\n- Alternatively, migrate to `Poseidon2Sponge`, which is safe for variable-length inputs due to its length-encoding IV.\n\n## References\n- [circom Poseidon implementation](https://github.com/iden3/circomlib/blob/master/circuits/poseidon.circom) — reference implementation where `nInputs` determines `T`\n- [Poseidon paper](https://eprint.iacr.org/2019/458) — Section 4 discusses sponge construction and padding requirements","published":"2026-03-12T17:47:10.717Z","modified":"2026-10-28T02:30:35.940141488Z","cvss":null,"epss":{"score":0.00221,"percentile":0.12866,"asOf":"2026-08-19"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"crates.io","name":"soroban-poseidon","fixedVersion":"25.0.1"}],"fix":{"url":"https://github.com/stellar/rs-soroban-poseidon/pull/10","label":"stellar/rs-soroban-poseidon#10"},"references":[{"type":"WEB","url":"https://github.com/stellar/rs-soroban-poseidon/releases/tag/v25.0.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32129.json"},{"type":"ADVISORY","url":"https://github.com/stellar/rs-soroban-poseidon/security/advisories/GHSA-g2p6-hh5v-7hfm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-32129"},{"type":"FIX","url":"https://github.com/stellar/rs-soroban-poseidon/pull/10"},{"type":"WEB","url":"https://github.com/stellar/rs-soroban-poseidon/commit/ceb20d3593fc4a8a951a7e99d8fa2344f8250a8c"},{"type":"PACKAGE","url":"https://github.com/stellar/rs-soroban-poseidon"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:35.940141488Z"}}