Vulnerability in H3

CVE-2026-33128

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.

Vulnerability class: CRLF Injection

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N.

EPSS exploit prediction

EPSS: 0.007 (50.7th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 51st percentile — 50.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-33128: held from 0.006 to 0.007.

EPSS over last 30 days · oldest: 0.006 · newest: 0.007 · change: +0.001

Affected products

  • H3 — versions 2.0.0, 2.0.1
  • H3js H3 — versions >= 2.0.0, < 2.0.1-rc.15, < 1.15.6

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-33128?
CVE-2026-33128 is a high-severity vulnerability in H3, classified under CRLF Injection. CVSS score: 7.5/10. Published 2026-03-20.
How severe is CVE-2026-33128?
High severity. CVSS v3 base score is 7.5 out of 10.