Poseidon V1 variable-length input collision via implicit zero-padding

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

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 · score source

EPSS

• CVE-2026-32129: 0.21% estimated exploitation activity in the next 30 days; percentile 11.83 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 poseidonhash 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 = inputlen << 64), making different-length inputs produce distinct states. Patches Fixed by enforcing inputs.len() == RATE in PoseidonSponge::computehash, 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…

Published by the source

13 Mar 2026, 15:40 UTC

Last modified by the source

13 Mar 2026, 15:40 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-g2p6-hh5v-7hfm

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# Patch Next advisory brief: CVE-2026-32129

Advisory: Poseidon V1 variable-length input collision via implicit zero-padding
IDs: CVE-2026-32129, GHSA-g2p6-hh5v-7hfm
Record: https://patchnext.com/advisories/cve-2026-32129 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: soroban-poseidon 25.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io soroban-poseidon: affected < 25.0.1; fixed in 25.0.1

## Suggested inspection (read-only)
- crates.io soroban-poseidon: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on soroban-poseidon.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-g2p6-hh5v-7hfm (GitHub-reviewed advisory GHSA-g2p6-hh5v-7hfm lists affected ranges: crates.io soroban-poseidon >=0 <25.0.1)

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