CVE-2026-33128
High
Description
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.
SeverityHigh
CVSS7.5
Exploit probability—
ProductH3
PublishedMar 20, 2026
First seenMar 20, 2026
Weakness typeCWE-93CWE-93
How to fix
Update
- h3 h31.15.6 or later
- h32.0.1-rc.15, 1.15.6 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| h3 h3 | v < 1.15.6, 2.0.0, 2.0.1 | 1.15.6 |
| h3npm | 2.0.0 ≤ v < 2.0.1-rc.15, v < 1.15.6 | 2.0.1-rc.15, 1.15.6 |
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