GHSA-VJ64-RJF3-W3V7
Vulnerability from github – Published: 2026-05-21 20:24 – Updated: 2026-06-11 14:05Impact
- Key:
challenger/src/multi_field_challenger.rs|MultiField32Challenger::duplexing|transcript_malleability - Affected files:
challenger/src/multi_field_challenger.rs,field/src/helpers.rs -
Violated invariant: The Fiat-Shamir sponge must bind challenges to the exact sequence of observed field elements. Specifically: (1) absorption must be injective — distinct observation streams must produce distinct sponge states, (2) squeezing must be injective — distinct PF rate cells must yield distinct F challenge sequences, and (3) all bits of each absorbed PF element must influence the sponge state.
-
Exploit scenario: An attacker controlling prover-side observations can craft distinct transcripts that produce identical challenges, breaking the binding property of Fiat-Shamir. Three independent attack vectors exist:
-
Partial-chunk aliasing (absorb):
duplexing()packsinput_buffer.chunks(num_f_elms)viareduce_32(base 2^32) with no length marker and no zeroing of unused rate slots. Observing[x]followed by a sample yields the same sponge state as[x, 0, ..., 0](padded tonum_f_elms) followed by a sample, sincereduce_32treats missing high limbs identically to explicit zeros. The attacker can extend or truncate the tail of any observation batch without changing future challenges. -
Non-injective squeeze (squeeze):
split_32decomposes each PF rate cell into base-2^64 digits and maps each throughTF::from_u64, which reduces modF::ORDER(~2^31). Two distinct PF values whose base-2^64 digits differ only in their upper 33 bits produce identical F challenge sequences. This weakens the entropy of sampled challenges and can enable selective forgery when the attacker can influence the sponge state pre-squeeze. -
High-bit truncation (observe Hash/MerkleCap):
num_f_elms = PF::bits() / 64computes the number of F limbs per PF element. For BN254 (254-bit field), this yields 3 limbs covering 192 bits — the top 62 bits of every digest word are silently discarded. An attacker can find two distinct BN254 hash digests that differ only in bits 192–253 and observe them interchangeably without affecting challenges. -
Evidence: In
duplexing(), the absorb path (reduce_32with base 2^32) and the squeeze path (split_32with base 2^64) use incompatible radices with no length domain separation.reduce_32is a plain Horner foldacc * 2^32 + digitwith no padding or tag, so trailing zeros are free.split_32extracts u64 digits and casts each viaTF::from_u64, which performs modular reduction, collapsing the top bits. The limb countPF::bits() / 64is a floor division that silently drops all bits beyond64 * num_f_elmsfor fields whose bit-width is not a multiple of 64.
Patches
Included in v0.4.3 and v0.5.3
{
"affected": [
{
"package": {
"ecosystem": "crates.io",
"name": "p3-challenger"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.4.3"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "crates.io",
"name": "p3-challenger"
},
"ranges": [
{
"events": [
{
"introduced": "0.5.0"
},
{
"fixed": "0.5.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-46654"
],
"database_specific": {
"cwe_ids": [
"CWE-1240",
"CWE-345"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-21T20:24:21Z",
"nvd_published_at": "2026-06-10T22:16:59Z",
"severity": "HIGH"
},
"details": "### Impact\n\n- **Key**: `challenger/src/multi_field_challenger.rs` | `MultiField32Challenger::duplexing` | `transcript_malleability`\n- **Affected files**: `challenger/src/multi_field_challenger.rs`, `field/src/helpers.rs`\n- **Violated invariant**: The Fiat-Shamir sponge must bind challenges to the exact sequence of observed field elements. Specifically: (1) absorption must be injective \u2014 distinct observation streams must produce distinct sponge states, (2) squeezing must be injective \u2014 distinct PF rate cells must yield distinct F challenge sequences, and (3) all bits of each absorbed PF element must influence the sponge state.\n\n- **Exploit scenario**: An attacker controlling prover-side observations can craft distinct transcripts that produce identical challenges, breaking the binding property of Fiat-Shamir. Three independent attack vectors exist:\n\n 1. **Partial-chunk aliasing (absorb)**: `duplexing()` packs `input_buffer.chunks(num_f_elms)` via `reduce_32` (base 2^32) with no length marker and no zeroing of unused rate slots. Observing `[x]` followed by a sample yields the same sponge state as `[x, 0, ..., 0]` (padded to `num_f_elms`) followed by a sample, since `reduce_32` treats missing high limbs identically to explicit zeros. The attacker can extend or truncate the tail of any observation batch without changing future challenges.\n\n 2. **Non-injective squeeze (squeeze)**: `split_32` decomposes each PF rate cell into base-2^64 digits and maps each through `TF::from_u64`, which reduces mod `F::ORDER` (~2^31). Two distinct PF values whose base-2^64 digits differ only in their upper 33 bits produce identical F challenge sequences. This weakens the entropy of sampled challenges and can enable selective forgery when the attacker can influence the sponge state pre-squeeze.\n\n 3. **High-bit truncation (observe Hash/MerkleCap)**: `num_f_elms = PF::bits() / 64` computes the number of F limbs per PF element. For BN254 (254-bit field), this yields 3 limbs covering 192 bits \u2014 the top 62 bits of every digest word are silently discarded. An attacker can find two distinct BN254 hash digests that differ only in bits 192\u2013253 and observe them interchangeably without affecting challenges.\n\n- **Evidence**: In `duplexing()`, the absorb path (`reduce_32` with base 2^32) and the squeeze path (`split_32` with base 2^64) use incompatible radices with no length domain separation. `reduce_32` is a plain Horner fold `acc * 2^32 + digit` with no padding or tag, so trailing zeros are free. `split_32` extracts u64 digits and casts each via `TF::from_u64`, which performs modular reduction, collapsing the top bits. The limb count `PF::bits() / 64` is a floor division that silently drops all bits beyond `64 * num_f_elms` for fields whose bit-width is not a multiple of 64.\n\n### Patches\n\nIncluded in v0.4.3 and v0.5.3",
"id": "GHSA-vj64-rjf3-w3v7",
"modified": "2026-06-11T14:05:27Z",
"published": "2026-05-21T20:24:21Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/Plonky3/Plonky3/security/advisories/GHSA-vj64-rjf3-w3v7"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-46654"
},
{
"type": "PACKAGE",
"url": "https://github.com/Plonky3/Plonky3"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N",
"type": "CVSS_V4"
}
],
"summary": "Plonky3 MultiField32Challenger: transcript malleability and challenge entropy loss"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.