CVE-2021-21259Public exploitNetwork attack vector

Arbitrary JavaScript execution via slide dependencies

Published Jan 22, 2021 · Updated Aug 3, 2024

Stored XSS in HedgeDoc before 1.7.2 allows attackers to execute arbitrary JavaScript when a crafted note is opened in slide mode. Slide YAML accepts JavaScript dependencies, while reveal-markdown replaces script end tags case-sensitively and permitted JSONP scripts process injected DOM content. Note creation or editing can be unauthenticated under some configurations, but execution requires a user to view the malicious note as slides.

CVSS severity7.4
High
EPSS probability1.35%
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

Stored XSS in HedgeDoc before 1.7.2 allows attackers to execute arbitrary JavaScript when a crafted note is opened in slide mode. Slide YAML accepts JavaScript dependencies, while reveal-markdown replaces script end tags case-sensitively and permitted JSONP scripts process injected DOM content. Note creation or editing can be unauthenticated under some configurations, but execution requires a user to view the malicious note as slides.

The record

CVE
CVE-2021-21259
Published
Jan 22, 2021
Updated
Aug 3, 2024
Vendor
HedgeDoc
Product
HedgeDoc
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=< 1.7.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

HedgeDoc · HedgeDocversion=< 1.7.2

Published CVSS scores

7.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:H/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

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