High 7.5Published Mar 20, 2026

CVE-2026-33128h3 has a Server-Sent Events Injection via Unsanitized Newlines in Event Stream Fields

Updated under an hour ago (Oct 26, 2026, 10:30 PM ET)

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It affects h3js h3 and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for h3js h3

Exploited in the last 30 days

H3 is a minimal H(TTP) framework. In versions prior to 1.15.6 and between 2.0.0 through 2.0.1-rc.14, createEventStream is vulnerable to Server-Sent Events (SSE) injection due to missing newline sanitization in formatEventStreamMessage() and formatEventStreamComment(). An attacker who controls any part of an SSE message field (id, event, data, or comment) can inject arbitrary SSE events to connected clients. This issue is fixed in versions 1.15.6 and 2.0.1-rc.15.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
Weakness (CWE): CWE-93
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Mar 20, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

h3js h3 h3js:h3 (from the name)	from 2.0.0, < 2.0.1-rc.15; before 1.15.6	CNA record
h3 h3 h3:h3	before 1.15.6; 2.0.0; 2.0.1; 2.0.1; 2.0.1; 2.0.1; 2.0.1; 2.0.1; and 7 more ranges	NVD

References

References

https://github.com/h3js/h3/security/advisories/GHSA-22cc-p3c6-wpvm	x-refsource-confirm, exploit, vendor-advisory
https://github.com/h3js/h3/commit/7791538e15ca22437307c06b78fa155bb73632a6	x-refsource-misc, patch
https://github.com/h3js/h3/blob/52c82e18bb643d124b8b9ec3b1f62b081f044611/src/utils/internal/event-stream.ts#L170-L187	x-refsource-misc, product

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.