CVE catalog

CVE-2026-18040

Severity: Medium · CVSS 5.9CVSS:4.0/AV:L/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 3, 2026, 8:55:06 AM UTC
Updated: Oct 3, 2026, 9:17:04 AM UTC
Source: [NVD] · [CVE record]
EPSS: 0.11% · Oct 25, 2026

In Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged.

Vulnerable and fixed packages

Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.

Distribution	Package	Release	Version	Status
Debian	bouncycastle	sid	`1.86.2-1`	fixed
Debian	bouncycastle	forky	`1.86-1`	fixed
Debian	bouncycastle	trixie	`1.80-3`	vulnerable
Debian	bouncycastle	bookworm	`1.72-2`	vulnerable

Fixed-version evidence

Distribution	Package	Type	Release	Fixed version	Urgency	Origin	Bugs
Debian	bouncycastle	source	sid	`1.86-1`	not yet assigned	Not reported	Not reported
Debian	bouncycastle	source	forky	`1.86-1`	not yet assigned	Not reported	Not reported
Debian	bouncycastle	source	trixie	`(unfixed)`	not yet assigned	Not reported	Not reported
Debian	bouncycastle	source	bookworm	`(unfixed)`	not yet assigned	Not reported	Not reported

OpenFactory catalog packages

[Debian 12 (Bookworm)]

[libbcjmail-java]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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]Affected
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, 7:46:37 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]