Vulnerability in H3js H3
CVE-2026-86252
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.004 (28.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 29th percentile — 28.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.001
Affected products
Weakness classification (CWE)
References
- github.com/h3js/h3/security/advisories/GHSA-4hxc-9384-m385 (vendor-advisory)
- www.vulncheck.com/advisories/h3-before-1.15.9-sse-event-injection-via-carriage-… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-86252?
- CVE-2026-86252 is a medium-severity vulnerability in H3js H3, classified under Improper Neutralization of Special Elements in Output Used by a Downstream Component (Injection). CVSS score: 5.3/10. Published 2026-09-06.
- How severe is CVE-2026-86252?
- Medium severity. CVSS v3 base score is 5.3 out of 10.