CVE-2026-21883Public exploitNetwork attack vector

Session hijacking via prefix-matched WebSocket origins

Published Jan 8, 2026 · Updated Jan 8, 2026

Cross-site WebSocket hijacking in Bokeh before 3.8.2 allows remote attackers to access server sessions through a malicious origin. The match_host function in src/bokeh/server/util.py compares hostname segments with zip(), but never rejects a host containing extra trailing segments, so an allowlisted prefix passes validation. Exploitation requires a deployed server with an origin allowlist and a victim visiting an attacker-controlled site; authentication hooks and network boundaries remain enforced.

CVSS severity5.4
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site WebSocket hijacking in Bokeh before 3.8.2 allows remote attackers to access server sessions through a malicious origin. The match_host function in src/bokeh/server/util.py compares hostname segments with zip(), but never rejects a host containing extra trailing segments, so an allowlisted prefix passes validation. Exploitation requires a deployed server with an origin allowlist and a victim visiting an attacker-controlled site; authentication hooks and network boundaries remain enforced.

The record

CVE
CVE-2026-21883
Published
Jan 8, 2026
Updated
Jan 8, 2026
Vendor
Bokeh
Product
Bokeh
Classifications
CWE-1385, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 8, 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.

  1. Affected versionversion=< 3.8.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Bokeh · Bokehversion=< 3.8.2

Published CVSS scores

5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
4.5GitHub, Inc.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

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1385Missing Origin Validation in WebSockets
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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