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CVE Record

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

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.

MediumCVSS 4.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2026-21883 affects Bokeh server applications before 3.8.2. A flawed WebSocket origin allowlist check can trust attacker-controlled lookalike domains. If a user is lured to such a site, the site may connect to the Bokeh server as that user and interact with data or visualizations.

Executive priority

Treat as a moderate-priority update for teams using Bokeh dashboards. Prioritize systems exposing sensitive analytics or internal data. The issue requires user interaction, but successful abuse could affect confidentiality and integrity of dashboard sessions.

Technical view

Bokeh versions 3.8.1 and below perform incomplete Origin validation for WebSocket connections. An allowed origin such as dashboard.corp may incorrectly match dashboard.corp.attacker.com. The issue is classified as CWE-1385 and has CVSS 4.0 score 4.5. Version 3.8.2 fixes the validation logic.

Likely exposure

Exposure is likely limited to organizations running Bokeh server applications below 3.8.2 with origin allowlists configured. Risk increases where dashboards expose sensitive data, are reachable by users' browsers, or rely on WebSocket origin checks for cross-site protection.

Exploitation context

Sources describe a user-interaction scenario: an attacker must control or use a matching-lookalike domain and lure a victim to visit it. The source bundle does not indicate CISA KEV listing or confirmed active exploitation.

Researcher notes

The available advisory describes origin suffix-style matching leading to WebSocket hijacking conditions. Evidence supports affected versions below 3.8.2 and a fix commit. No public source in the bundle confirms active exploitation. Avoid assuming exposure unless Bokeh server and relevant origin allowlists are present.

Mitigation direction

  • Upgrade Bokeh to version 3.8.2 or later.
  • Review Bokeh server origin allowlist settings for exact intended hostnames.
  • Follow the GitHub security advisory and vendor guidance.
  • Restrict access to sensitive Bokeh apps where feasible.

Validation and detection

  • Inventory applications using Bokeh server.
  • Confirm installed Bokeh versions are 3.8.2 or later.
  • Review server configuration for allowed WebSocket origins.
  • Check whether sensitive dashboards are exposed to user browsers.
  • Monitor vendor advisories for updated guidance.
Prepared
Confidence
high
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-1385: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-21883 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
4.5 (4.0)
Known Exploited
No
Published

Vector: 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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
4.5CVSS 4.0MediumCVSS: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——Primary CVE score

Vulnerability scoring details

Base CVSS 4.0 score

4.5Medium
CVSS 4.0 vector shape for CVE-2026-21883Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: 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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
bokehbokeh< 3.8.2Listed
Weakness

CWE details

CWE-1385

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-1385 · source CWE mapping

Missing Origin Validation in WebSockets

Missing Origin Validation in WebSockets represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs