CVE catalog

CVE-2026-18036

In Bouncy Castle for Java before 1.86, NTRU reduced…

In Bouncy Castle for Java before 1.86, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately division-free, so each reduction was carried out by an integer division whose latency depends on the secret operand. Polynomial.modQ divided by a variable divisor, which a compiler cannot strength-reduce to a multiply the way it can a constant one, so it emitted a division on every call including on the decapsulation path where the dividend derives from the private key; Polynomial.mod3 and NTRUSampling.mod3 divided the secret key polynomials f and g during key generation, the message polynomials r and m during encapsulation, and coefficients recovered during decapsulation. An attacker able to measure that timing can recover information about the NTRU private key. modQ now masks, which is exact because q is always a power of two, and mod3 uses the reference implementation's division-free fold and select; the results are unchanged.

Severity: High · CVSS 8.2CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber
Published: Oct 1, 2026, 10:00:00 PM UTC
Updated: Oct 2, 2026, 8:17:01 AM UTC
Source: [NVD] · [CVE record]
EPSS: 0.28% · Oct 27, 2026

Projects and upstream resources

[bouncycastle][Source-reported homepage]

Reported versions and fixes

Each observation applies to its named package, distribution, and release. Distribution backports can fix a vulnerability while retaining an older upstream version number.

Version impact has not been established. The original provider fields are retained below.

Provider details and historical evidence

Original provider fields

{
  "package_releases": [
    {
      "name": "bouncycastle",
      "status": "fixed",
      "release": "sid",
      "version": "1.86.2-1"
    },
    {
      "name": "bouncycastle",
      "status": "fixed",
      "release": "forky",
      "version": "1.86-1"
    },
    {
      "name": "bouncycastle",
      "status": "vulnerable",
      "release": "trixie",
      "version": "1.80-3"
    },
    {
      "name": "bouncycastle",
      "status": "vulnerable",
      "release": "bookworm",
      "version": "1.72-2"
    }
  ],
  "fixed_versions": [
    {
      "bug": null,
      "name": "bouncycastle",
      "type": "source",
      "origin": null,
      "release": "sid",
      "urgency": "not yet assigned",
      "fixed_version": "1.86-1"
    },
    {
      "bug": null,
      "name": "bouncycastle",
      "type": "source",
      "origin": null,
      "release": "forky",
      "urgency": "not yet assigned",
      "fixed_version": "1.86-1"
    },
    {
      "bug": null,
      "name": "bouncycastle",
      "type": "source",
      "origin": null,
      "release": "trixie",
      "urgency": "not yet assigned",
      "fixed_version": ""
    },
    {
      "bug": null,
      "name": "bouncycastle",
      "type": "source",
      "origin": null,
      "release": "bookworm",
      "urgency": "not yet assigned",
      "fixed_version": ""
    }
  ],
  "distribution_packages": []
}

OpenFactory catalog packages

Matching against OpenFactory catalog package versions is in progress.

[Debian 12 (Bookworm)]

[libbcjmail-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcmail-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcpg-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcpkix-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcprov-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbctls-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcutil-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12

[Debian 13 (Trixie)]

[libbcjmail-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcmail-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcpg-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcpkix-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcprov-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbctls-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcutil-java]Unknown
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13

Observed: Oct 23, 2026, 7:46:40 PM UTC

References

[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX]