Eclipse Langium up to 4.4.0 IndentationAwareTokenBuilder algorithmic complexity

Summaryinfo

A vulnerability marked as problematic has been reported in Eclipse Langium up to 4.4.0. This affects the function IndentationAwareTokenBuilder. This manipulation causes algorithmic complexity. This vulnerability is handled as CVE-2026-124683. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability classified as problematic was found in Eclipse Langium up to 4.4.0. Affected by this vulnerability is the function IndentationAwareTokenBuilder. The manipulation with an unknown input leads to a algorithmic complexity vulnerability. The CWE definition for the vulnerability is CWE-407. An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached. As an impact it is known to affect availability. The summary by CVE is:

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.

It is possible to read the advisory at gitlab.eclipse.org. This vulnerability is known as CVE-2026-124683 since 11/09/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• Eclipse

Name

• Langium

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4.0

License

• open-source

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