Eclipse Langium versions 3.2.0 through 4.4.0 contain an inefficient algorithmic complexity issue (CWE-407) in the opt-in IndentationAwareTokenBuilder and IndentationAwareLexer. When producing DEDENT tokens, the token builder recomputes line numbers by re-scanning the entire preceding document text. A document whose indentation changes on most lines then takes quadratic time to tokenize. Because tokenization is synchronous, a crafted document of a few hundred kilobytes can block the Node.js event loop for tens of seconds. That causes a DoS for every user served by the same process. Languages built with the DefaultLexer and DefaultTokenBuilder are unaffected.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
Eclipse Foundation Eclipse Langium unaffected
Version Status Constraints
3.2.0 affected ≤ 4.4.0

No data.

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Project Subscriptions

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Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/eclipse-langium/langium/security/advisories/GHSA-297v-g8mm-qj4h cve-icon cve-icon
https://gitlab.eclipse.org/security/cve-assignment/-/work_items/553 cve-icon cve-icon
https://gitlab.eclipse.org/security/vulnerability-reports/-/work_items/1069 cve-icon cve-icon
History

Mon, 09 Nov 2026 17:45:00 +0000

Type Values Removed Values Added
Title Inefficient Algorithmic Complexity Causes Denial of Service in Eclipse Langium

Mon, 09 Nov 2026 16:30:00 +0000

Type Values Removed Values Added
Description Eclipse Langium versions 3.2.0 through 4.4.0 contain an inefficient algorithmic complexity issue (CWE-407) in the opt-in IndentationAwareTokenBuilder and IndentationAwareLexer. When producing DEDENT tokens, the token builder recomputes line numbers by re-scanning the entire preceding document text. A document whose indentation changes on most lines then takes quadratic time to tokenize. Because tokenization is synchronous, a crafted document of a few hundred kilobytes can block the Node.js event loop for tens of seconds. That causes a DoS for every user served by the same process. Languages built with the DefaultLexer and DefaultTokenBuilder are unaffected.
Weaknesses CWE-407
References
Metrics cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: eclipse

Published:

Updated: 2026-11-09T16:47:45.873Z

Reserved: 2026-11-09T10:36:46.112Z

Link: CVE-2026-124683

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-11-09T17:17:27.690

Modified: 2026-11-09T17:17:27.690

Link: CVE-2026-124683

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-11-09T17:30:08Z

Weaknesses