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CVE-2026-49851— Mistune: Potential DoS via quadratic-time parsing in parse_link_text

Quick assessment

Affected
lepture mistune
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.

lepture mistune是lepture的Markdown解析库。 lepture mistune 3.3.0之前版本存在资源管理错误漏洞，该漏洞源于parse_link_text函数中超线性（约O(n²)）行为，可能导致CPU耗尽拒绝服务攻击。

CVSS 8.7 · High EPSS 0.63% · P50

Possible ATT&CK Techniques 1 AI

T1499.002 · Service Exhaustion Flood

Affected Version Matrix 1

VendorProduct Version RangeStatus
lepture mistune < 3.3.0 affected
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I. Basic Information for CVE-2026-49851

Vulnerability Information
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Vulnerability Title
Mistune: Potential DoS via quadratic-time parsing in parse_link_text
Source: CVE Program / CVE List V5
Vulnerability Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
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
Vulnerability Title
lepture mistune 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
lepture mistune是lepture的Markdown解析库。 lepture mistune 3.3.0之前版本存在资源管理错误漏洞，该漏洞源于parse_link_text函数中超线性（约O(n²)）行为，可能导致CPU耗尽拒绝服务攻击。
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-2026-49851

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III. Intelligence Information for CVE-2026-49851

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Vendor Advisories for CVE-2026-49851 (1)

IV. Related Vulnerabilities

Same product: mistune
Same vendor: lepture
Same weakness: CWE-400