What’s Vulnerable › Vulnerabilities

CVE-2020-26239: Cross-Site Scripting in Scratch browser addons

• Severity: medium (CVSS 5.4 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: 2020-11-23 · updated 2026-06-17
• Weakness: CWE-79

Description

Scratch Addons is a WebExtension that supports both Chrome and Firefox. Scratch Addons before version 1.3.2 is vulnerable to DOM-based XSS. If the victim visited a specific website, the More Links addon of the Scratch Addons extension used incorrect regular expression which caused the HTML-escaped values to be unescaped, leading to XSS. Scratch Addons version 1.3.2 fixes the bug. The extension will be automatically updated by the browser. More Links addon can be disabled via the option of the extension.

Affected products

• ScratchAddons: before 1.3.2 — fixed in 1.3.2

How to fix

Upgrade to a fixed version: ScratchAddons 1.3.2. Check the vendor advisory for mitigations.

References

• https://github.com/ScratchAddons/ScratchAddons/blob/a471893df403f86c9182970678175d4772a0690c/addons/more-links/userscript.js#L15
• https://github.com/ScratchAddons/ScratchAddons/commit/b9a52d6532c8514254c7cc1d8e18710dbedc41ff
• https://github.com/ScratchAddons/ScratchAddons/releases/tag/v1.3.2
• https://github.com/ScratchAddons/ScratchAddons/security/advisories/GHSA-6qfq-px3r-xj4p
• https://github.com/ScratchAddons/ScratchAddons/blob/a471893df403f86c9182970678175d4772a0690c/addons/more-links/userscript.js#L15
• https://github.com/ScratchAddons/ScratchAddons/commit/b9a52d6532c8514254c7cc1d8e18710dbedc41ff
• https://github.com/ScratchAddons/ScratchAddons/releases/tag/v1.3.2
• https://github.com/ScratchAddons/ScratchAddons/security/advisories/GHSA-6qfq-px3r-xj4p

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