# 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.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Mar 2026
- **Updated:** 13 Mar 2026
- **Also known as:** GHSA-g2p6-hh5v-7hfm

## 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 (Use of Weak Hash)

## Which versions are affected by CVE-2026-32129?

2 open source packages ship an affected version, including soroban-poseidon.


| Package | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-32129 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-32129 in the wild and no public exploit code.

Affected packages and fixed versions:
- soroban-poseidon (crates.io): affected all versions; fixed in 25.0.1
- soroban-poseidon (crates.io): affected all versions; fixed in 25.0.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-32129/ (Markdown: https://insights.sbomify.com/CVE-2026-32129/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-32129
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-32129
- OSV: https://osv.dev/vulnerability/CVE-2026-32129

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-32129/
Summaries are generated and may contain mistakes; the official description above is the record.