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CVE-2026-86252— h3 before 1.15.9 SSE Event Injection via Carriage Return

Quick assessment

Affected
h3js h3
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

H3 在 1.15.9 之前的版本未能对 EventStream 数据字段和注释字段中的回车符（CR, \r）进行清理（sanitization），这使得攻击者可以通过包含未清理的回车符来注入任意 SSE（服务器发送事件）事件。攻击者可以利用这一点来注入事件类型指令、将单次 push 调用拆分为多个浏览器解析的事件，或从注释字段中逃逸以注入数据，从而绕过此前仅针对换行符（\n）注入问题的 CVE 修复。

CVSS 5.3 · Medium

Affected Version Matrix 4

VendorProduct Version RangeStatus
h3js h3 < 1.15.9 affected
1.15.9 unaffected
2.0.0-beta.0< 2.0.1-rc.17 affected
2.0.1-rc.17 unaffected
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I. Basic Information for CVE-2026-86252

Vulnerability Information
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Vulnerability Title
h3 before 1.15.9 SSE Event Injection via Carriage Return
Source: CVE Program / CVE List V5
Vulnerability Description
h3 versions before 1.15.9 fail to sanitize carriage return characters in EventStream data and comment fields, allowing attackers to inject arbitrary SSE events by including unsanitized carriage returns. Attackers can inject event type directives, split single push calls into multiple browser-parsed events, or escape comment fields to inject data, bypassing the prior CVE fix that only addressed newline injection.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
输出中的特殊元素转义处理不恰当(注入)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
h3js h3 0 ~ 1.15.9 -

II. Public POCs for CVE-2026-86252

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III. Intelligence Information for CVE-2026-86252

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Vendor Advisories for CVE-2026-86252 (2)

Same Patch Batch · h3js · 2026-09-06 · 5 CVEs total

CVE-2026-86250 7.5 HIGH h3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked Cookie
CVE-2026-86251 5.9 MEDIUM h3 before 1.15.9 Path Traversal via Double Decoding
CVE-2026-86253 5.9 MEDIUM h3 before 1.15.6 Path Traversal via Percent-Encoded Dot Segments
CVE-2026-86205 5.4 MEDIUM h3 before 2.0.1-rc.18 Open Redirect via redirectBack()

IV. Related Vulnerabilities

Same product: h3
Same vendor: h3js
Same weakness: CWE-74

V. Comments for CVE-2026-86252

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