Security Digest · Vulnerability record
CVE-2026-12866: expr-eval vulnerable to Code Execution
All versions of the package expr-eval are vulnerable to Code Execution via the toJSFunction() API.
CVSS 9.2 Critical EPSS 0.9% · p58
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.9%, percentile 58: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 58% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
expr-eval(npm) <= 2.0.2, no fixed version listed;org.webjars.npm:expr-eval(Maven) <= 2.0.2, no fixed version listed. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
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.
Weakness type: CWE-94.
Product: expr-eval (npm) · Assigned by: snyk · Published: 2026-06-23
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| npm | expr-eval | <= 2.0.2 | none listed |
| Maven | org.webjars.npm:expr-eval | <= 2.0.2 | none listed |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| n/a | expr-eval | < * |
| n/a | org.webjars.npm:expr-eval | < * |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| snyk | 4.0 | 9.2 Critical | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N |
| snyk | 3.1 | 9.8 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| GitHub | 4.0 | 9.2 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Attack requirements: present (depends on deployment conditions)
- Privileges required: none (no login)
- User interaction: none
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.87% probability of exploitation activity in the next 30 days; percentile 58.
Timeline
- — CVE record published by snyk
- — GitHub-reviewed advisory GHSA-q9v2-7m5w-4693 published (critical)
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-q9v2-7m5w-4693 github.com
- CVE.org record CVE-2026-12866 cve.org
- NVD entry CVE-2026-12866 nvd.nist.gov
Other references from the CVE record and advisory
- security.snyk.io security.snyk.io
- security.snyk.io security.snyk.io
- github.com github.com
- github.com github.com
- github.com github.com