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Multiple timing variability issues in operations intended to be constant-time

Type: advisorySources: OSV

## Summary Several operations intended to be constant-time could execute secret-dependent branches, depending on the compiler and target CPU. These include subtraction, zero counting, division, and Montgomery multiplication. Additionally, `UintRef` equality could terminate at the first unequal limb, and `BoxedMontyForm::invert` branched on whether an inverse exists. ## Impact Applications using affected operations on secret integers may leak information through timing or microarchitectural side channels. This includes information about intermediate arithmetic values, matching limbs, and invertibility. Such leakage could potentially enable recovery of cryptographic secrets. Practical exploitability depends on the downstream algorithm, compiler, target CPU, and an attacker's ability to observe the side channel. ## Resolution Upgrade to v0.7.6, which removes the identified branches, updates `ctutils` to include its constant-time fixes, and adds BINSEC-based regression checks using `cargo checkct` for arithmetic on multiple targets.

Products
crypto-bigint
Affected versions
Not specified
Fixed versions
0.7.6
CVEs
Not specified
Confirmed fixed CVEs
Not specified
Updated in this feed
1 Nov 2026, 03:39 UTC · Revision 1

Source evidence

Multiple timing variability issues in operations intended to be constant-time

core-osv · Original source

Published 23 Oct 2026, 12:00 UTC

## Summary Several operations intended to be constant-time could execute secret-dependent branches, depending on the compiler and target CPU. These include subtraction, zero counting, division, and Montgomery multiplication. Additionally, `UintRef` equality could terminate at the first unequal limb, and `BoxedMontyForm::invert` branched on whether an inverse exists. ## Impact Applications using affected operations on secret integers may leak information through timing or microarchitectural side channels. This includes information about intermediate arithmetic values, matching limbs, and invertibility. Such leakage could potentially enable recovery of cryptographic secrets. Practical exploitability depends on the downstream algorithm, compiler, target CPU, and an attacker's ability to observe the side channel. ## Resolution Upgrade to v0.7.6, which removes the identified branches, updates `ctutils` to include its constant-time fixes, and adds BINSEC-based regression checks using `cargo checkct` for arithmetic on multiple targets.

osv:RUSTSEC-2026-0387

crypto-bigint

Fixed versions: 0.7.6

Complete source record
{
  "id": "593bd75e2e2d36cb649c766f83d534f0723e13206bebd63fd9d02ba2f6ee0a26",
  "url": "https://osv.dev/vulnerability/RUSTSEC-2026-0387",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Multiple timing variability issues in operations intended to be constant-time",
    "summary": "## Summary Several operations intended to be constant-time could execute secret-dependent branches, depending on the compiler and target CPU. These include subtraction, zero counting, division, and Montgomery multiplication. Additionally, `UintRef` equality could terminate at the first unequal limb, and `BoxedMontyForm::invert` branched on whether an inverse exists. ## Impact Applications using affected operations on secret integers may leak information through timing or microarchitectural side channels. This includes information about intermediate arithmetic values, matching limbs, and invertibility. Such leakage could potentially enable recovery of cryptographic secrets. Practical exploitability depends on the downstream algorithm, compiler, target CPU, and an attacker's ability to observe the side channel. ## Resolution Upgrade to v0.7.6, which removes the identified branches, updates `ctutils` to include its constant-time fixes, and adds BINSEC-based regression checks using `cargo checkct` for arithmetic on multiple targets.",
    "evidence": "osv:RUSTSEC-2026-0387",
    "products": [
      {
        "name": {
          "value": "crypto-bigint",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "0.7.6",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "RUSTSEC-2026-0387",
      "aliases": [
        "RUSTSEC-2026-0387"
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.0.0-0"
                },
                {
                  "fixed": "0.7.6"
                }
              ]
            }
          ],
          "package": {
            "name": "crypto-bigint",
            "purl": "pkg:cargo/crypto-bigint",
            "ecosystem": "crates.io"
          },
          "database_specific": {
            "cvss": null,
            "source": "https://github.com/rustsec/advisory-db/blob/osv/crates/RUSTSEC-2026-0387.json",
            "categories": [
              "crypto-failure"
            ],
            "informational": null
          },
          "ecosystem_specific": {
            "affects": {
              "os": [],
              "arch": [],
              "functions": []
            },
            "affected_functions": null
          }
        }
      ],
      "modified": "2026-10-24T03:45:02.365137418Z",
      "provider": "osv",
      "references": [
        "https://crates.io/crates/crypto-bigint",
        "https://rustsec.org/advisories/RUSTSEC-2026-0387.html",
        "https://github.com/RustCrypto/crypto-bigint/pull/1365"
      ],
      "provider_metadata": {
        "license": "CC-BY-4.0"
      }
    },
    "related_cves": [],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 428188,
  "published_at": "2026-10-23T12:00:00+00:00"
}