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CVE-2026-59928— Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions

Quick assessment

Affected
lepture mistune
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.

Hsiaoming Yang mistune是日本Hsiaoming Yang个人开发者的一个快速、可扩展的Markdown解析器。 Hsiaoming Yang mistune 3.3.0之前版本存在资源管理错误漏洞，该漏洞源于对Markdown文档中重复或不同的参考链接定义处理不当，在src/mistune/block_parser.py和ref_links环境字典处理中导致二次方工作量，容易受到拒绝服务攻击，通过CPU耗尽实现。

CVSS 7.5 · High EPSS 0.41% · P35

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
lepture mistune < 3.3.0 affected
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I. Basic Information for CVE-2026-59928

Vulnerability Information
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Vulnerability Title
Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions
Source: CVE Program / CVE List V5
Vulnerability Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links environment dictionary handling, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.
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
算法复杂性
Source: CVE Program / CVE List V5
Vulnerability Title
Hsiaoming Yang mistune 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Hsiaoming Yang mistune是日本Hsiaoming Yang个人开发者的一个快速、可扩展的Markdown解析器。 Hsiaoming Yang mistune 3.3.0之前版本存在资源管理错误漏洞，该漏洞源于对Markdown文档中重复或不同的参考链接定义处理不当，在src/mistune/block_parser.py和ref_links环境字典处理中导致二次方工作量，容易受到拒绝服务攻击，通过CPU耗尽实现。
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
lepture mistune < 3.3.0 -

II. Public POCs for CVE-2026-59928

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Qwen3.6-35B-A3B · 9932 chars
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Exploit chain & mitigation
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III. Intelligence Information for CVE-2026-59928

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Patches & Fixes for CVE-2026-59928 (1)

Vendor Advisories for CVE-2026-59928 (1)

Vendor Pages for CVE-2026-59928 (1)

Same Patch Batch · lepture · 2026-07-08 · 9 CVEs total

CVE-2026-59922 7.5 HIGH Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `
CVE-2026-59925 7.5 HIGH inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs
CVE-2026-59923 6.1 MEDIUM Mistune: XSS via percent-encoded javascript URI bypass in safe_url()
CVE-2026-59929 6.1 MEDIUM Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes
CVE-2026-59924 5.9 MEDIUM Mistune: Arbitrary File Read via Include directive path traversal
CVE-2026-59927 5.3 MEDIUM Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `Rec
CVE-2026-59930 4.3 MEDIUM Mistune toc / TableOfContents directive: heading IDs use predictable `toc_N` numbering wit
CVE-2026-59926 Mistune: XSS via unescaped class option in Admonition directive

IV. Related Vulnerabilities

Same product: mistune
Same vendor: lepture
Same weakness: CWE-407

V. Comments for CVE-2026-59928

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