CVE-2026-124683

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.

• https://github.com/eclipse-langium/langium/security/advisories/GHSA-297v-g8mm-qj4h

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

• HIGHCVE-2019-25781PoC
• HIGHCVE-2026-100700PoC
• HIGHCVE-2026-101021PoC
• MEDIUMCVE-2026-102277PoC
• MEDIUMCVE-2026-102461PoC
• HIGHCVE-2026-102994PoC
• HIGHCVE-2026-102997PoC
• HIGHCVE-2026-102999PoC

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