CVE-2026-18040

MEDIUMPre-NVD 5.95.9
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This medium-severity CVE scores 5.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.1% (1st percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source

Also known asEUVD-2026-92004 (ENISA EUVD) · GHSA-rxw8-22c7-wgq6 (GitHub Security Advisories)Source: ENISA EUVD

5.9EG
EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.1%CVSS: 5.9Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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.

CVSS
5.9
EG Score
5.9MEDIUMmedium confidence
EG Risk
27
EG Risk 27/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity59% × 45%
Impact severity (EG Severity): CVSS 5.9 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.1% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.1%
EPSS %ILE
1st
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (5.9): severity, escalated by confirmed exploitation. This CVE's 5.9 is its impact severity (EG Severity), not escalated.

EG Severity
5.9 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source
EG Likelihood
0.1% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-10). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

October 3, 2026

Last Modified

October 6, 2026

Advisory Details (1)

Auto-updated Oct 3, 2026
Patch available.
Web page

CVE‐2026‐18040 · bcgit/bc-java Wiki · GitHub

https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018040

Vendor Advisories for CVE-2026-18040(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
bouncycastle1.72-2 ... 1.86-1 (6 versions)
  • every version on: no fix on record
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
bouncycastle1.80-3, 1.86-1
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
bouncycastle1.80-3
  • every version up to 1.86-1: fixed in 1.86-1
—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 8× in last 7d / 30× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed its CVE.org record (CNA or CISA ADP). An arrow marks a change the record states ("CVSS → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). "EchelonGraph re-scored" is our own recompute of this CVE's score, not an update from a source, and is not counted in the refreshes above. Most recent first.

  1. 2026-11-12 16:33 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  2. 2026-11-11 16:38 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  3. 2026-11-11 07:35 UTCEchelonGraph re-scored
  4. 2026-11-11 07:35 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6 · GitHub severity MODERATE
  5. 2026-11-10 16:42 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  6. 2026-11-09 16:34 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  7. 2026-11-08 16:38 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  8. 2026-11-07 16:38 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  9. 2026-11-06 16:37 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  10. 2026-11-05 16:37 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  11. 2026-11-04 16:35 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  12. 2026-11-04 01:53 UTCEchelonGraph re-scored
  13. 2026-11-04 01:53 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6 · GitHub severity MODERATE
  14. 2026-11-03 16:47 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  15. 2026-11-02 16:44 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  16. 2026-11-01 16:34 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  17. 2026-10-31 16:32 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  18. 2026-10-30 16:33 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  19. 2026-10-29 16:00 UTCEchelonGraph re-scored
  20. 2026-10-29 16:00 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  21. 2026-10-28 16:31 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  22. 2026-10-27 16:31 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  23. 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  24. 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  25. 2026-10-25 14:45 UTCEchelonGraph re-scored
Show 48 more
  1. 2026-10-23 06:00 UTCEchelonGraph re-scored
  2. 2026-10-23 06:00 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  3. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  4. 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  5. 2026-10-20 16:32 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  6. 2026-10-19 16:31 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  7. 2026-10-18 03:59 UTCEchelonGraph re-scored
  8. 2026-10-17 16:33 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  9. 2026-10-16 16:40 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  10. 2026-10-15 16:31 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  11. 2026-10-14 16:32 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  12. 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  13. 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  14. 2026-10-12 16:28 UTCEchelonGraph re-scored
  15. 2026-10-11 20:08 UTCEchelonGraph re-scored
  16. 2026-10-11 17:20 UTCEchelonGraph re-scored
  17. 2026-10-11 15:33 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  18. 2026-10-11 14:52 UTCEchelonGraph re-scored
  19. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  20. 2026-10-10 19:59 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  21. 2026-10-10 15:33 UTCEchelonGraph re-scored
  22. 2026-10-10 15:33 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  23. 2026-10-09 20:06 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  24. 2026-10-09 15:30 UTCEchelonGraph re-scored
  25. 2026-10-09 15:30 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  26. 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  27. 2026-10-08 15:29 UTCEchelonGraph re-scored
  28. 2026-10-08 15:28 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  29. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  30. 2026-10-07 14:51 UTCEchelonGraph re-scored
  31. 2026-10-07 14:51 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  32. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  33. 2026-10-06 14:51 UTCEchelonGraph re-scored
  34. 2026-10-06 14:51 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  35. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  36. 2026-10-05 16:28 UTCEchelonGraph re-scored
  37. 2026-10-05 16:28 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  38. 2026-10-05 16:11 UTCEchelonGraph re-scored
  39. 2026-10-05 16:11 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  40. 2026-10-05 09:24 UTCEchelonGraph re-scored
  41. 2026-10-05 09:24 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  42. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  43. 2026-10-04 09:25 UTCEchelonGraph re-scored
  44. 2026-10-04 09:25 UTCGHSA enrichmentGHSA-rxw8-22c7-wgq6
  45. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.1% · 1st percentile
  46. 2026-10-03 09:25 UTCEchelonGraph re-scored
  47. 2026-10-03 09:05 UTCEchelonGraph re-scoredFirst assessed: 5.9 MEDIUM
  48. 2026-10-03 09:04 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-18040?
CVE-2026-18040 is a medium-severity vulnerability; its CVE record was published on October 3, 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…
When was the CVE record for CVE-2026-18040 published?
The CVE record for CVE-2026-18040 was published on October 3, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of October 6, 2026; the record at its source may have been updated since.
Is CVE-2026-18040 actively exploited?
CVE-2026-18040 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.1% probability of exploitation in the next 30 days (1st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-18040?
CVE-2026-18040 has a CVSS base score of 5.9 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-18040?
A fix for CVE-2026-18040 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-18040 are linked in the Vendor Advisories panel on this page.

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