CVE-2026-86818

MEDIUMPre-NVD 4.84.8
EchelonGraph scoreMEDIUM confidence

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

Score 4.8 from GitHub Security Advisory (severity: MODERATE) published 2026-09-29. A secondary CVSS source baseline 4.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source
Trending — 4 sources updated this week

Also known asEUVD-2026-78403 (ENISA EUVD) · GHSA-jvvf-x445-j334 (GitHub Security Advisories)Source: ENISA EUVD

4.8EG
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: 0.3%CVSS: 4.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

fast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv, that added a mailto scheme parser in version 4.1.3. In versions 4.1.3 and 4.1.4, the mailto parser compares each query field name to the reserved names to, subject, and body while the name is still percent-encoded, and decodes it only when storing it as a generic header, so a percent-encoded spelling of a reserved field name is not recognized as that field at parse time but is re-emitted as the literal field name when the parsed URI is serialized. An application that validates, logs, or displays the recipient list from the first parse and then serializes the URI and sends it can silently gain an attacker-chosen recipient, and the subject and body fields can be smuggled across the same roundtrip. The issue is fixed in fast-uri 4.1.5, and users should upgrade to 4.1.5 or later. As a workaround, do not act on a mailto URI that fast-uri has re-serialized without first decoding and re-validating its recipient, subject, and body fields.

CVSS v3
4.8
EG Score
4.8MEDIUMmedium confidence
EG Risk
22
EG Risk 22/100

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)
Severity48% × 45%
Impact severity (EG Severity): CVSS 4.8 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.2% × 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
0.3%
EPSS %ILE
16th
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 (4.8): severity, escalated by confirmed exploitation. This CVE's 4.8 is its impact severity (EG Severity), not escalated.

EG Severity
4.8 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-31). 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

September 15, 2026

Last Modified

September 16, 2026

Advisory Details (2)

Auto-updated Sep 15, 2026
Patch available. Sources: github.
Web page

Security Advisories | OpenJS Foundation CVE Numbering Authority

https://cna.openjsf.org/security-advisories.html
GitHub advisoryMentions a patch (unverified)

fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization · Advisory · fastify/fast-uri · GitHub

https://github.com/fastify/fast-uri/security/advisories/GHSA-jvvf-x445-j334

Vendor Advisories for CVE-2026-86818(1)

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

Patch Availability(1)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
npmfast-uri @ 4.1.5 (fixes >= 4.1.3, < 4.1.5)—ghsa

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(3 across 3 ecosystems)
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
node-ajv8.12.0~ds+~2.1.1-5 ... 8.20.0~ds+~cs7.1.6-1 (15 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
node-ajv8.12.0~ds+~2.1.1-5 ... 8.20.0~ds+~cs7.1.5-1 (14 versions)
  • every version up to 8.20.0~ds+~cs7.1.6-1: fixed in 8.20.0~ds+~cs7.1.6-1
—
npm(1)
PackageVulnerable rangeFix by version rangeDependents
fast-uri—
  • 4.1.3 up to 4.1.5: fixed in 4.1.5
—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 10× in last 7d / 46× 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 it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 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). Most recent first.

  1. 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  2. 2026-11-01 07:38 UTCGHSA enrichmentGHSA-jvvf-x445-j334 · GitHub severity MODERATE · GitHub CVSS 4.8
  3. 2026-11-01 07:38 UTCEG score recompute
  4. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  5. 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  6. 2026-10-29 23:25 UTCOSV refresh
  7. 2026-10-29 16:34 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  8. 2026-10-28 16:33 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  9. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  10. 2026-10-26 16:32 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  11. 2026-10-25 16:34 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  12. 2026-10-25 13:54 UTCEG score recompute
  13. 2026-10-24 16:34 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  14. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  15. 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  16. 2026-10-22 12:41 UTCEG score recompute
  17. 2026-10-21 16:34 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  18. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  19. 2026-10-19 16:33 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  20. 2026-10-18 16:33 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  21. 2026-10-18 03:04 UTCEG score recompute
  22. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  23. 2026-10-16 16:44 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  24. 2026-10-15 16:33 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  25. 2026-10-14 16:34 UTCEPSS rescoreEPSS 0.3% · 15th percentile
Show 55 more
  1. 2026-10-13 16:35 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  2. 2026-10-12 16:35 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  3. 2026-10-12 14:51 UTCEG score recompute
  4. 2026-10-11 19:16 UTCEG score recompute
  5. 2026-10-11 16:33 UTCEG score recompute
  6. 2026-10-11 13:50 UTCEG score recompute
  7. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  8. 2026-10-11 05:44 UTCEG score recompute
  9. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  10. 2026-10-10 03:30 UTCEG score recompute
  11. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  12. 2026-10-09 02:06 UTCEG score recompute
  13. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  14. 2026-10-08 00:41 UTCEG score recompute
  15. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  16. 2026-10-06 23:17 UTCEG score recompute
  17. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  18. 2026-10-05 21:54 UTCEG score recompute
  19. 2026-10-05 17:44 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  20. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  21. 2026-10-03 18:52 UTCEG score recompute
  22. 2026-10-02 17:28 UTCEG score recompute
  23. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  24. 2026-10-01 16:04 UTCEG score recompute
  25. 2026-09-30 15:04 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  26. 2026-09-30 14:41 UTCEG score recompute
  27. 2026-09-29 12:47 UTCEG score recompute
  28. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  29. 2026-09-28 11:23 UTCEG score recompute
  30. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  31. 2026-09-27 09:59 UTCEG score recompute
  32. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  33. 2026-09-26 08:35 UTCEG score recompute
  34. 2026-09-25 07:11 UTCEG score recompute
  35. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.3% · 14th percentile
  36. 2026-09-24 05:47 UTCEG score recompute
  37. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.2% · 5th percentile
  38. 2026-09-23 04:23 UTCEG score recompute
  39. 2026-09-22 16:01 UTCEPSS rescoreEPSS 0.2% · 5th percentile
  40. 2026-09-22 02:59 UTCEG score recompute
  41. 2026-09-21 21:09 UTCEPSS rescoreEPSS 0.2% · 5th percentile
  42. 2026-09-21 01:35 UTCEG score recompute
  43. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.2% · 5th percentile
  44. 2026-09-20 00:11 UTCEG score recompute
  45. 2026-09-18 22:46 UTCEG score recompute
  46. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.2% · 5th percentile
  47. 2026-09-17 21:22 UTCEG score recompute
  48. 2026-09-17 19:32 UTCEPSS rescoreEPSS 0.2% · 5th percentile
  49. 2026-09-16 14:57 UTCEG score recompute
  50. 2026-09-16 14:09 UTCEPSS rescoreEPSS 0.2% · 5th percentile
  51. 2026-09-15 13:33 UTCEG score recompute
  52. 2026-09-15 12:40 UTCEG score recompute
  53. 2026-09-15 11:29 UTCEG score recompute
  54. 2026-09-15 10:50 UTCEG score recomputeFirst assessed: 4.8 MEDIUM
  55. 2026-09-15 10:47 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-86818?
CVE-2026-86818 is a medium-severity vulnerability; its CVE record was published on September 15, 2026. fast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv, that added a mailto scheme parser in version 4.1.3. In versions 4.1.3 and 4.1.4, the mailto parser compares each query field name to the reserved names to, subject, and body while the name is still…
When was the CVE record for CVE-2026-86818 published?
The CVE record for CVE-2026-86818 was published on September 15, 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 September 16, 2026; the record at its source may have been updated since.
Is CVE-2026-86818 actively exploited?
CVE-2026-86818 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (16th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-86818?
CVE-2026-86818 has a CVSS base score of 4.8 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-86818?
A fix for CVE-2026-86818 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-86818 are linked in the Vendor Advisories panel on this page.

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