Bokeh server applications have Incomplete Origin Validation in WebSockets

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

4.5 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U · score source

EPSS

• CVE-2026-21883: 0.18% estimated exploitation activity in the next 30 days; percentile 7.16 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

This vulnerability allows for Cross-Site WebSocket Hijacking (CSWSH) of a deployed Bokeh server instance. Scope This vulnerability is only relevant to deployed Bokeh server instances. There is no impact on static HTML output, standalone embedded plots, or Jupyter notebook usage. This vulnerability does not prevent any requirements for up-front authentication on Bokeh servers that have authentication hooks in place, and cannot be used to make Bokeh servers deployed on private, internal networks accessible outside those networks. Impact If a Bokeh 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…

Published by the source

6 Jan 2026, 17:53 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-793v-589g-574v

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-793v-589g-574v

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# Patch Next advisory brief: CVE-2026-21883

Advisory: Bokeh server applications have Incomplete Origin Validation in WebSockets
IDs: CVE-2026-21883, GHSA-793v-589g-574v
Record: https://patchnext.com/advisories/cve-2026-21883 (revision 3, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: bokeh 3.8.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI bokeh: affected < 3.8.2; fixed in 3.8.2

## Suggested inspection (read-only)
- `python -m pip show bokeh`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on bokeh.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-793v-589g-574v (OSV record GHSA-793v-589g-574v lists affected ranges: PyPI bokeh >=0 <3.8.2 (fixed))
- Verified: https://github.com/advisories/GHSA-793v-589g-574v (GitHub-reviewed advisory GHSA-793v-589g-574v lists affected ranges: PyPI bokeh >=0 <3.8.2)

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