CVE-2026-12866 — expr-eval
CRITICALCVE-2026-12866 is a critical-severity (CVSS 9.8) Code Injection vulnerability in org.webjars.npm:expr-eval. No vendor fix is recorded yet; mitigation options are listed below.
expr-eval vulnerable to Code Execution
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-12866.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-12866 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
expr-evalnpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.webjars.npm:expr-eval | all versions | No fix |
| 📦npm | expr-eval | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.webjars.npm:expr-eval, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of org.webjars.npm:expr-eval has shipped for CVE-2026-12866 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
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…
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.Source: Red Hat security advisory for CVE-2026-12866 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-12866 in your dependencies?
Find it across Maven, npm, including transitive dependencies.