RCE in Expr-Eval

CVE-2026-12866

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.

Vulnerability class: RCE (Remote Code Execution)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.009 (57.2th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 57th percentile — 57.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-12866: held from 0.009 to 0.009.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

  • Expr-Eval — versions 0
  • Org.webjars.npm:expr-Eval — versions 0

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-12866?
CVE-2026-12866 is a critical-severity vulnerability in Expr-Eval, classified under Code Injection. CVSS score: 9.8/10. Published 2026-06-23.
How severe is CVE-2026-12866?
Critical severity. CVSS v3 base score is 9.8 out of 10.