CVE-2026-33128
H3 ≤ 1.15.6
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:NSummary
CVE-2026-33128 is a high-severity CRLF Injection (CWE-93) vulnerability in H3 H3. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Content Injection (T1659); ranked at the 44th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-33128 is a Server-Sent Events (SSE) injection vulnerability in the H3 minimal HTTP framework, specifically affecting the createEventStream function due to missing newline sanitization in formatEventStreamMessage() and formatEventStreamComment(). The flaw impacts H3 versions prior to 1.15.6 and those between 2.0.0 through 2.0.1-rc.14. It is rated 7.5 on the CVSS 3.1 scale (AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N) and maps to CWE-93 (Improper Neutralization of CRLF Sequences).
An attacker who controls any part of an SSE message field—such as id, event, data, or comment—can inject arbitrary SSE events that are delivered to connected clients. Exploitation requires network access and high attack complexity but no privileges or user interaction, with scope changing to enable low confidentiality impact and high integrity impact through injected events.
The H3 GitHub security advisory (GHSA-22cc-p3c6-wpvm) and related commit detail the fix, implemented in versions 1.15.6 and 2.0.1-rc.15 via proper sanitization. Security practitioners should upgrade affected H3 instances to these patched releases to mitigate the issue.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-13666
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V4.2.4
Mitigating Controls (NIST 800-53 r5) AI
Input validation directly stops untrusted data containing CRLF sequences from reaching the component that treats CRLF as a delimiter.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require input neutralization and validation to block CRLF injection.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can detect CRLF flaws but does not itself implement the neutralization.
Secure development lifecycle mandates input validation and output encoding that directly prevents CRLF injection.
Application security requirements include rules for neutralizing special characters such as CRLF in inputs.
Secure architecture principles encourage safe handling of untrusted data but do not prescribe specific CRLF controls.
Secure coding standards explicitly require neutralization of CRLF sequences, fully addressing this weakness.