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CVE-2026-4671— justhtml before 1.18.0 Denial of Service via CSS Selector

Quick assessment

Affected
EmilStenstrom justhtml
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

JustHTML 1.18.0 之前的版本在 CSS 选择器处理和链接化处理方面存在多个低严重性的拒绝服务（DoS）漏洞。如果应用程序执行以下操作：评估由攻击者控制的选择器字符串（通过 query()、matches() 或基于选择器的转换）、在未受信任的大型文档上运行选择器匹配、从不信任的结构构建 DOM 树，或对攻击者控制的文本启用链接化处理，则可能导致异常高的 CPU 或内存消耗。 触发条件包括： 选择器过大 选择器列表过大 复合选择器过大 组合符链过长 功能性伪类嵌套过深 标记或位置匹配重复 循环 DOM

CVSS 7.5 · High

Affected Version Matrix 2

VendorProduct Version RangeStatus
EmilStenstrom justhtml < 1.18.0 affected
1.18.0 unaffected
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I. Basic Information for CVE-2026-4671

Vulnerability Information
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Vulnerability Title
justhtml before 1.18.0 Denial of Service via CSS Selector
Source: CVE Program / CVE List V5
Vulnerability Description
justhtml before 1.18.0 contains multiple low-severity denial-of-service issues in CSS selector handling and linkification. Applications that evaluate attacker-controlled selector strings (via query(), matches(), or selector-based transforms), run selector matching over very large untrusted documents, construct DOM trees from untrusted structure, or enable linkification over attacker-controlled text may consume disproportionate CPU or memory. Triggers include oversized selectors, large selector lists, oversized compound selectors, long combinator chains, deeply nested functional pseudo-classes, repeated token/positional matching, cyclic DOM graphs causing non-terminating traversal, and punctuation-heavy or trailing-bracket linkification input. These are availability-only concerns and do not by themselves allow script execution, data disclosure, or sanitizer bypass. Default JustHTML(sanitize=True) usage is not expected to be exposed, since selectors are normally supplied by application code.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
EmilStenstrom justhtml 0 ~ 1.18.0 -

II. Public POCs for CVE-2026-4671

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
Success marker: VULNERABLE: justhtml <1.18.0 CSS-selector DoS confirmed - attacker selector query burned 5033 ms CPU vs 0 ms for a benign selector on the same document (amplification 5033x)
Reproduction recording is a Pro+ exclusive
Watch the full sandbox build + live exploit recording for this CVE. Limited-time ¥499/mo.
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claude_code · 11868 chars
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III. Intelligence Information for CVE-2026-4671

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Vendor Advisories for CVE-2026-4671 (2)

Same Patch Batch · EmilStenstrom · 2026-08-23 · 11 CVEs total

CVE-2026-7808 9.8 CRITICAL justhtml before 1.16.0 Multiple Security Issues via Sanitization
CVE-2026-8445 9.8 CRITICAL justhtml before 1.12.0 Sanitizer Bypass via Markdown
CVE-2026-5388 9.8 CRITICAL justhtml before 1.15.0 Multiple Security Issues
CVE-2026-9769 7.5 HIGH justhtml before 1.10.0 Denial of Service via deeply nested HTML
CVE-2026-77088 6.1 MEDIUM justhtml 0.9.0 through 1.21.0 Cross-Site Scripting via code-span
CVE-2026-74793 6.1 MEDIUM justhtml before 3.11.0 XSS via selectedcontent projection
CVE-2026-6827 6.1 MEDIUM justhtml before 1.17.0 Multiple Cross-Site Scripting Vulnerabilities
CVE-2026-8630 6.1 MEDIUM justhtml before 1.12.0 Mutation XSS via Raw Text Elements
CVE-2026-5751 6.1 MEDIUM justhtml before 1.14.0 Mutation XSS via custom sanitization policies
CVE-2026-5389 6.1 MEDIUM justhtml before 1.13.0 XSS via code fence breakout

IV. Related Vulnerabilities

Same product: justhtml
Same vendor: EmilStenstrom
Same weakness: CWE-400

V. Comments for CVE-2026-4671

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