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Advisory severityMedium4.2Vendor: LowRed Hat Linux

Medium [CVE-2026-12866] Code Execution via crafted expressions in toJSFunction API

This medium-severity Red Hat Linux advisory covers CVE-2026-12866 affecting Red Hat Enterprise Linux AI (RHEL AI) 3.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

CVE-2026-12866 Source published Source updated

VulniPulse record published Record updated

CVE-2026-12866
Affected products & platforms
Red Hat LinuxUnclassified
Open source advisory

Summary

All versions of the package expr-eval are vulnerable to Code Execution via the toJSFunction() API. An attacker can execute arbitrary JavaScript by supplying crafted expressions that are compiled into native code using new Function().

Because user-controlled expressions are transformed directly into executable JavaScript, attackers can escape the intended expression sandbox and run arbitrary code within the application's context. A remote attacker can exploit this vulnerability by supplying crafted expressions to the toJSFunction() API.

RHEL AI 3.4 bootc images ship [email protected] as a dependency of @langchain/community. The only identified consumer is the LangChain Calculator tool, which calls Parser.evaluate() and does not invoke toJSFunction().

CVE-2026-12866 affects only the toJSFunction() API. No other npm package in the image depends on expr-eval.

For this reason the issue is rated Low for RHEL AI. Red Hat severity: Low — CVSS 4.2 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N).

Weakness: CWE-917. Affected Red Hat products: Red Hat Enterprise Linux AI (RHEL AI) 3.

Red Hat does not currently list a fixing RHSA for this CVE.

Is CVE-2026-12866 exploited?

No exploitation is reported in the sources VulniPulse tracks: CVE-2026-12866 is not in the CISA KEV catalog (checked ) and this advisory does not report exploitation. That is not proof the vulnerability cannot be exploited.

How do I fix CVE-2026-12866?

The advisory VulniPulse tracks names no fixed release. Follow Red Hat's guidance for workarounds and updates.

Confirm against the vendor advisory before you patch.

Affected versions

No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

Fixed versions

No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • LangChainJS already replaced expr-eval with math-expression-evaluator in a later @langchain/community release (fix for CVE-2025-12735). Bootc owners should bump @langchain/community to a version that no longer bundles expr-eval, which removes the dead dependency entirely.

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

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