CVE-2026-86252

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreHIGH confidence

Score 5.3 from GitHub Security Advisory published 2026-09-06. a secondary CVSS source baseline 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this weekElevated
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

h3 versions before 1.15.9 fail to sanitize carriage return characters in EventStream data and comment fields, allowing attackers to inject arbitrary SSE events by including unsanitized carriage returns. Attackers can inject event type directives, split single push calls into multiple browser-parsed events, or escape comment fields to inject data, bypassing the prior CVE fix that only addressed newline injection.

CVSS v3
5.3
EG Score
5.3(high)
EG Risk
55(Attend)
EG Risk 55/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity53% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
12%
KEV
Not listed

Published

September 6, 2026

Last Modified

September 8, 2026

Advisory Details (2)

Auto-updated Sep 6, 2026
🔬 Proof of concept available. Patch available. Sources: github.
generic

h3 before 1.15.9 SSE Event Injection via Carriage Return | Advisories | VulnCheck

https://www.vulncheck.com/advisories/h3-before-1.15.9-sse-event-injection-via-carriage-return
github Patch Available🟡 PoC Available

SSE Event Injection via Unsanitized Carriage Return (`\r`) in EventStream Data and Comment Fields (Bypass of CVE Fix) · Advisory · h3js/h3 · GitHub

https://github.com/h3js/h3/security/advisories/GHSA-4hxc-9384-m385

Vendor Advisories for CVE-2026-86252(1)

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

Affected Packages

(1 across 1 ecosystem)
npm(1)
PackageVulnerable rangeFixed inDependents
h3—2.0.1-rc.17—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 18× in last 7d / 37× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. 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. Most recent first.

  1. 2026-09-18 19:28 UTCEPSS rescore
  2. 2026-09-18 16:14 UTCEG score recompute
  3. 2026-09-18 16:14 UTCGHSA enrichment
  4. 2026-09-17 19:32 UTCEPSS rescore
  5. 2026-09-17 13:44 UTCEG score recompute
  6. 2026-09-17 13:44 UTCGHSA enrichment
  7. 2026-09-16 14:09 UTCEPSS rescore
  8. 2026-09-16 11:40 UTCEG score recompute
  9. 2026-09-16 11:40 UTCGHSA enrichment
  10. 2026-09-16 05:15 UTCEPSS rescore
  11. 2026-09-15 09:37 UTCEG score recompute
  12. 2026-09-15 09:37 UTCGHSA enrichment
  13. 2026-09-15 03:12 UTCEPSS rescore
  14. 2026-09-15 03:12 UTCEPSS rescore
  15. 2026-09-14 07:33 UTCEG score recompute
  16. 2026-09-14 07:33 UTCGHSA enrichment
  17. 2026-09-13 05:30 UTCEG score recompute
  18. 2026-09-13 05:30 UTCGHSA enrichment
  19. 2026-09-12 03:27 UTCEG score recompute
  20. 2026-09-12 03:27 UTCGHSA enrichment
  21. 2026-09-11 14:53 UTCEPSS rescore
  22. 2026-09-11 14:53 UTCEPSS rescore
  23. 2026-09-11 01:23 UTCEG score recompute
  24. 2026-09-11 01:23 UTCGHSA enrichment
  25. 2026-09-09 23:19 UTCEG score recompute
Show 12 more
  1. 2026-09-09 23:19 UTCGHSA enrichment
  2. 2026-09-08 22:01 UTCEPSS rescore
  3. 2026-09-08 20:13 UTCGHSA enrichment
  4. 2026-09-08 16:51 UTCEG score recompute
  5. 2026-09-08 16:50 UTCGHSA enrichment
  6. 2026-09-08 16:04 UTCEG score recompute
  7. 2026-09-08 16:04 UTCGHSA enrichment
  8. 2026-09-07 14:36 UTCEG score recompute
  9. 2026-09-07 14:36 UTCGHSA enrichment
  10. 2026-09-06 12:22 UTCEG score recompute
  11. 2026-09-06 12:12 UTCEG score recompute
  12. 2026-09-06 12:09 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-86252?
CVE-2026-86252 is a medium vulnerability published on September 6, 2026. h3 versions before 1.15.9 fail to sanitize carriage return characters in EventStream data and comment fields, allowing attackers to inject arbitrary SSE events by including unsanitized carriage returns. Attackers can inject event type directives, split single push calls into multiple browser-parsed…
When was CVE-2026-86252 disclosed?
CVE-2026-86252 was first published in the National Vulnerability Database on September 6, 2026, with the most recent update on September 8, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-86252 actively exploited?
CVE-2026-86252 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 87.7% of all scored CVEs.
What is the CVSS score of CVE-2026-86252?
CVE-2026-86252 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-86252?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-86252, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-86252

Explore →

Is Your Infrastructure Affected by CVE-2026-86252?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs