What’s Vulnerable › Vulnerabilities

CVE-2026-21883: Bokeh server applications have Incomplete Origin Validation in WebSockets

• Severity: medium (CVSS 5.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-01-08 · updated 2026-06-17
• Weakness: CWE-1385

Description

Bokeh is an interactive visualization library written in Python. In versions 3.8.1 and below, if a server is configured with an allowlist (e.g., dashboard.corp), an attacker can register a domain like dashboard.corp.attacker.com (or use a subdomain if applicable) and lure a victim to visit it. The malicious site can then initiate a WebSocket connection to the vulnerable Bokeh server. Since the Origin header (e.g., http://dashboard.corp.attacker.com/) matches the allowlist according to the flawed logic, the connection is accepted. Once connected, the attacker can interact with the Bokeh server on behalf of the victim, potentially accessing sensitive data, or modifying visualizations. This issue is fixed in version 3.8.2.

Affected products

• bokeh: before 3.8.2 — fixed in 3.8.2

How to fix

Upgrade to a fixed version: bokeh 3.8.2. Check the vendor advisory for mitigations.

References

• https://github.com/bokeh/bokeh/commit/cedd113b0e271b439dce768671685cf5f861812e
• https://github.com/bokeh/bokeh/security/advisories/GHSA-793v-589g-574v
• https://aydinnyunus.github.io/2026/01/24/bokeh-websocket-hijacking-cve-2026-21883/

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