Secuno
ENNL
Book demo

CVE-2026-33128

H3 vulnerability

7.5 HIGHPublic exploitEPSS 0.69%
  1. Published20 Mar 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityHigh
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityLow
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N

Affected products

H32.0.0 · 2.0.1 · < 1.15.6

Remediation

Fixed in
H3≥ 1.15.6

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

CVE-2026-829739.4
Improper neutralization of CRLF sequences in IMAP command construction in…
CVE-2026-1007179.9
froxlor is a server administration panel. In versions 2.3.10 and earlier,…
CVE-2026-551598.8
luci-app-adblock-fast a WebUI for fast, lightweight DNS-based ad-blocker for OpenWrt…
CVE-2026-405308.0
An improper neutralization of CRLF sequences ('CRLF injection') vulnerability in User…
CVE-2026-909379.9
froxlor versions before 2.2.5 fail to validate newline characters in subdomain redirect…
CVE-2026-480198.9
Laravel is a web application framework. Prior to versions 12.60.0 and 13.10.0, a CRLF…

Frequently asked

Is CVE-2026-33128 being actively exploited?

CVE-2026-33128 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.69%.

How severe is CVE-2026-33128?

CVE-2026-33128 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.69% probability of exploitation.

Which products are affected by CVE-2026-33128?

Affected products include H3.

How do I fix CVE-2026-33128?

Upgrade affected software to a fixed version, for example H3 1.15.6 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-33128 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation worksBook a demo

Get Patch this first every Monday

Five vulnerabilities that matter this week, ranked on real exploitation. Plain language, one email, no spam.

You can unsubscribe with one click from every issue. We handle your details as described in our privacy policy.

Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.