Summary
Poseidon V1 variable-length input collision via implicit zero-padding
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
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.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
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.
Frequently Asked Questions
- What is CVE-2026-32129? CVE-2026-32129 is a high-severity security vulnerability in soroban-poseidon (rust), affecting versions < 25.0.1. It is fixed in 25.0.1.
- Which versions of soroban-poseidon are affected by CVE-2026-32129? soroban-poseidon (rust) versions < 25.0.1 is affected.
- Is there a fix for CVE-2026-32129? Yes. CVE-2026-32129 is fixed in 25.0.1. Upgrade to this version or later.
- Is CVE-2026-32129 exploitable, and should I be worried? Whether CVE-2026-32129 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-32129 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-32129? Upgrade
soroban-poseidonto 25.0.1 or later.