CVE-2026-32129 — soroban-poseidon
Fix: stellar/rs-soroban-poseidon#10CVE-2026-32129 is a CWE-328 vulnerability in soroban-poseidon. A fix is available for soroban-poseidon — see the affected versions and patch details below.
Poseidon V1 variable-length input collision via implicit zero-padding
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-32129.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
soroban-poseidonReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
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, useT=3; to hash 1 input, useT=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 — reference implementation where
nInputsdeterminesT - Poseidon paper — Section 4 discusses sponge construction and padding requirements
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | soroban-poseidon | all versions | 25.0.1cargo update -p soroban-poseidon --precise 25.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for soroban-poseidon, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update soroban-poseidon to 25.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-32129 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-32129 in your dependencies?
Find it across crates.io, including transitive dependencies.