CVE-2020-26307Public exploitNetwork attack vector

Service hang via exponential HTML parser backtracking

Published Oct 26, 2024 · Updated Oct 28, 2024

Regular expression denial of service in HTML2Markdown 1.0.2 and earlier allows attackers to interrupt service via crafted HTML. The HTML parser's startTag and attr regular expressions perform exponential backtracking when repeated crafted attributes leave a tag incomplete. Any browser or Node.js application that passes attacker-controlled HTML to the converter can have its JavaScript execution monopolized, causing the hosting application to hang.

CVSS severity8.7
High
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Regular expression denial of service in HTML2Markdown 1.0.2 and earlier allows attackers to interrupt service via crafted HTML. The HTML parser's startTag and attr regular expressions perform exponential backtracking when repeated crafted attributes leave a tag incomplete. Any browser or Node.js application that passes attacker-controlled HTML to the converter can have its JavaScript execution monopolized, causing the hosting application to hang.

The record

CVE
CVE-2020-26307
Published
Oct 26, 2024
Updated
Oct 28, 2024
Vendor
Kates Gasis
Product
HTML2Markdown
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 26, 2024CVE publishedPublication date reported by the CVE source.
  2. Oct 28, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=1.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Kates Gasis · HTML2Markdownversion=0 <=1.0.2

Published CVSS scores

8.7GitHub CNACVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Green

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
T1499.004Application or System Exploitation Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo