# CVE-2026-12866: expr-eval vulnerable to Code Execution

> Attackers can execute arbitrary JavaScript code by supplying crafted expressions to the toJSFunction API, bypassing the intended sandbox.

- **Severity:** Critical 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Jun 2026
- **Updated:** 14 Aug 2026
- **Also known as:** CLSA-2026-1792241023, GHSA-q9v2-7m5w-4693, MINI-82jp-6mpf-372q, MINI-8j87-6r7x-pw3p, MINI-crgw-qrc7-vgc9, MINI-gj57-qfx6-6ff6, MINI-jqwp-gjvg-q6g9, MINI-vmp9-ccp6-r6gx, MINI-xgpx-xqwr-cpx6, ROOT-APP-NPM-CVE-2026-12866

## What is CVE-2026-12866?

CVE-2026-12866 is a critical code injection vulnerability in expr-eval, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-12866?

4 open source packages ship an affected version, including org.webjars.npm:expr-eval and expr-eval.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `org.webjars.npm:expr-eval` | Maven | All versions to 2.0.2 | None |
| `org.webjars.npm:expr-eval` | Maven | All versions to 2.0.2 | None |
| `expr-eval` | npm | All versions to 2.0.2 | None |
| `expr-eval` | npm | All versions to 2.0.2 | None |

## How do I fix CVE-2026-12866?

No fix published yet.

## Is CVE-2026-12866 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12866 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12866 and fix it if it is affected.

What it is: CVE-2026-12866 is a critical code injection vulnerability in expr-eval, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12866 exists.

Affected packages and fixed versions:
- org.webjars.npm:expr-eval (Maven): affected all versions up to 2.0.2; no fix listed
- org.webjars.npm:expr-eval (Maven): affected all versions up to 2.0.2; no fix listed
- expr-eval (npm): affected all versions up to 2.0.2; no fix listed
- expr-eval (npm): affected all versions up to 2.0.2; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-12866/ (Markdown: https://insights.sbomify.com/CVE-2026-12866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12866
- OSV: https://osv.dev/vulnerability/CVE-2026-12866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12866/
Summaries are generated and may contain mistakes; the official description above is the record.