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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是H3组织开源的一个HTTP框架。 H3 1.15.9之前版本和2.0.0-beta.0至2.0.1-rc.17之前版本存在输入验证错误漏洞，该漏洞源于未清理EventStream数据和注释字段中的回车字符，可能导致攻击者注入任意SSE事件。

CVSS 5.3 · Medium EPSS 0.36% · P29

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
Vulnerability Title
H3 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
H3是H3组织开源的一个HTTP框架。 H3 1.15.9之前版本和2.0.0-beta.0至2.0.1-rc.17之前版本存在输入验证错误漏洞，该漏洞源于未清理EventStream数据和注释字段中的回车字符，可能导致攻击者注入任意SSE事件。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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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