CVE-2026-32129: Soroban poseidon Poseidon V1 Variable-length Input Collision Vulnerability

HIGH
Advisory Identifier: GHSA-g2p6-hh5v-7hfm
Share
CWE-328
Published
Advisory Summary

CVE-2026-32129 is a HIGH poseidon v1 variable-length input collision vulnerability (CWE-328: Use of Weak Hash) affecting Soroban poseidon libraries in the crates.io ecosystem. The issue involves poseidon v1 variable-length input collision via implicit zero-padding. Remediation is available by upgrading affected packages to version 25.0.1.

CVE-2026-32129 at a Glance

CVE Identifier CVE-2026-32129
GHSA Identifier GHSA-g2p6-hh5v-7hfm
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-328: Use of Weak Hash
Affected Product Soroban poseidon
Package Ecosystem crates.io
Published Date
Last Updated

How to Fix CVE-2026-32129

To remediate this vulnerability, upgrade all affected Soroban poseidon dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

soroban-poseidon fixed: 25.0.1 
Upgrade soroban-poseidon to 25.0.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for soroban-poseidon

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-32129, inspect your project dependencies for Soroban poseidon:

inspect dependencies for soroban-poseidon

Analyze the terminal output to locate any version of Soroban poseidon in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 25.0.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-328: Use of Weak Hash, where the product uses an algorithm that produces a digest (output value) that does not meet security expectations for a hash function that allows an adversary to reasonably determine the original input (preimage attack), find another input that can produce the same hash (2nd preimage attack), or find multiple inputs that evaluate to the same hash (birthday attack). In Soroban poseidon, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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, use `T=3`; to hash 1 input, use `T=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](https://github.com/iden3/circomlib/blob/master/circuits/poseidon.circom) — reference implementation where `nInputs` determines `T` - [Poseidon paper](https://eprint.iacr.org/2019/458) — Section 4 discusses sponge construction and padding requirements

CVE-2026-32129 Affected Soroban poseidon Versions

1 component(s)
Fixed Versions:
25.0.1
Product / Package Ecosystem Affected Versions Fixed Version
soroban-poseidon
 crates.io
< 25.0.1
25.0.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/stellar/rs-soroban-poseidon/security/advisories/GHSA-g2p6-hh5v-7hfm
NVD — CVE-2026-32129 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-32129
Soroban poseidon Source Repository REPOSITORY
https://github.com/stellar/rs-soroban-poseidon/pull/10
Security Fix Commit FIX COMMIT
https://github.com/stellar/rs-soroban-poseidon/commit/ceb20d3593fc4a8a951a7e99d8fa2344f8250a8c
Soroban poseidon Source Repository REPOSITORY
https://github.com/stellar/rs-soroban-poseidon
Soroban poseidon Release RELEASE
https://github.com/stellar/rs-soroban-poseidon/releases/tag/v25.0.1

Frequently Asked Questions

What is CVE-2026-32129?
CVE-2026-32129 is a security vulnerability in Soroban poseidon involving Poseidon V1 variable-length input collision via implicit zero-padding under CWE-328: Use of Weak Hash.
Which Soroban poseidon versions are affected?
Affected versions include releases prior to 25.0.1 across affected packages: soroban-poseidon.
What version fixes CVE-2026-32129?
Upgrading to 25.0.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is soroban-poseidon affected?
Yes, soroban-poseidon is affected in releases prior to 25.0.1. Upgrade your dependency to 25.0.1 or later.
What CWE is associated with CVE-2026-32129?
CVE-2026-32129 is classified under CWE-328: Use of Weak Hash (The product uses an algorithm that produces a digest (output value) that does not meet security expectations for a hash function that allows an adversary to reasonably determine the original input (preimage attack), find another input that can produce the same hash (2nd preimage attack), or find multiple inputs that evaluate to the same hash (birthday attack).).
How can I check crates.io dependencies for CVE-2026-32129?
Run the dependency tree command: 'inspect dependencies for soroban-poseidon'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g2p6-hh5v-7hfm",
  "modified" : "2026-03-13T15:40:31Z",
  "published" : "2026-03-13T15:40:31Z",
  "aliases" : [ "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",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "soroban-poseidon"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "25.0.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "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" : "WEB",
    "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"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/stellar/rs-soroban-poseidon/releases/tag/v25.0.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-328" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-13T15:40:31Z",
    "nvd_published_at" : "2026-03-12T18:16:25Z"
  }
}