Local file theft via notebook output XSS
Published Sep 15, 2021 · Updated Aug 10, 2026
Cross-site scripting in Visual Studio Code before 1.59.1 allows attackers to read local files by inducing a user to open a crafted notebook. The built-in Jupyter Notebook renderer treats text/markdown cell output as HTML and runs embedded JavaScript without meaningful content-security restrictions. Opening the .ipynb file triggers the payload even in Restricted Mode; the demonstrated consequence is theft and remote exfiltration of files readable by the editor process.
Summary
What happened
Cross-site scripting in Visual Studio Code before 1.59.1 allows attackers to read local files by inducing a user to open a crafted notebook. The built-in Jupyter Notebook renderer treats text/markdown cell output as HTML and runs embedded JavaScript without meaningful content-security restrictions. Opening the .ipynb file triggers the payload even in Restricted Mode; the demonstrated consequence is theft and remote exfiltration of files readable by the editor process.
The record
- CVE
- CVE-2021-26437
- Published
- Sep 15, 2021
- Updated
- Aug 10, 2026
- Vendor
- Microsoft
- Product
- Visual Studio Code
- Classifications
- T1204.002
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 15, 2021CVE publishedPublication date reported by the CVE source.
- Aug 10, 2026Record 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.
- Affected versionversion=1.0.0 <1.59.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
- Visual Studio Code Jupyter Notebook RCE exploitfunctional · demonstrated
- Visual Studio Code .ipynb XSS arbitrary-file-read proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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