What’s Vulnerable › Vulnerabilities

CVE-2021-29503: Improper Neutralization of Script-Related HTML Tags in Notes

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-05-19 · updated 2026-06-17
• Weakness: CWE-80

Description

HedgeDoc is a platform to write and share markdown. HedgeDoc before version 1.8.2 is vulnerable to a cross-site scripting attack using the YAML-metadata of a note. An attacker with write access to a note can embed HTML tags in the Open Graph metadata section of the note, resulting in the frontend rendering the script tag as part of the `<head>` section. Unless your instance prevents guests from editing notes, this vulnerability allows unauthenticated attackers to inject JavaScript into notes that allow guest edits. If your instance prevents guests from editing notes, this vulnerability allows authenticated attackers to inject JavaScript into any note pages they have write-access to. This vulnerability is patched in version 1.8.2. As a workaround, one can disable guest edits until the next update.

Affected products

• hedgedoc: before 1.8.2 — fixed in 1.8.2

How to fix

Upgrade to a fixed version: hedgedoc 1.8.2. Check the vendor advisory for mitigations.

References

• https://github.com/hedgedoc/hedgedoc/commit/01dad5821ee28377ebe640c6c72c3e0bb0d51ea7
• https://github.com/hedgedoc/hedgedoc/releases/tag/1.8.2
• https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-gjg7-4j2h-94fq
• https://github.com/hedgedoc/hedgedoc/commit/01dad5821ee28377ebe640c6c72c3e0bb0d51ea7
• https://github.com/hedgedoc/hedgedoc/releases/tag/1.8.2
• https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-gjg7-4j2h-94fq

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