CVE-2021-29503Network attack vector

Stored XSS via unescaped Open Graph metadata

Published May 19, 2021 · Updated Aug 3, 2024

Stored cross-site scripting in HedgeDoc before 1.8.2 allows remote attackers with note write access to execute JavaScript in readers' browsers. The head.ejs template emits attacker-controlled Open Graph keys and values with EJS unescaped-output tags, placing injected HTML in the page head. Guest-editable notes permit unauthenticated injection; otherwise, authenticated note write access is required, and execution occurs when another user loads the note.

CVSS severity8.1
High
EPSS probability1.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in HedgeDoc before 1.8.2 allows remote attackers with note write access to execute JavaScript in readers' browsers. The head.ejs template emits attacker-controlled Open Graph keys and values with EJS unescaped-output tags, placing injected HTML in the page head. Guest-editable notes permit unauthenticated injection; otherwise, authenticated note write access is required, and execution occurs when another user loads the note.

The record

CVE
CVE-2021-29503
Published
May 19, 2021
Updated
Aug 3, 2024
Vendor
HedgeDoc
Product
HedgeDoc
Classifications
CWE-79, CWE-80, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 19, 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

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Is a vulnerable build present?

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

  1. Affected versionversion=< 1.8.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

HedgeDoc · HedgeDocversion=< 1.8.2

Published CVSS scores

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
8.1GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
T1189Drive-by Compromise

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

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Your stack

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