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CVE-2026-33128

CRITICALCVSS 10/10EPSS 0.49%

Last modified

CVE-2026-33128 is a critical-severity vulnerability rated 10/10 on the CVSS scale. 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(). EPSS estimates a 0.49% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
10/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS Probability
0.49%

38.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersionsUpdate
H3H3< 1.15.6—
H3H32.0.0—
H3H32.0.1Rc10

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is 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.
How severe is CVE-2026-33128?
CVE-2026-33128 has a CVSS score of 10/10 (CRITICAL severity). The EPSS model estimates a 0.49% probability of exploitation in the next 30 days.
How do I fix CVE-2026-33128?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-33128?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST