# CVE-2025-62494: Type confusion in string addition in QuickJS

> Type confusion in QuickJS string addition allows attackers to trigger memory corruption and execute arbitrary code via crafted JavaScript.

- **Severity:** High 7.1 (`CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 16 Oct 2025
- **Updated:** 16 Oct 2025
- **Also known as:** DEBIAN-CVE-2025-62494, GHSA-7gcv-76g2-94qm, UBUNTU-CVE-2025-62494

## What is CVE-2025-62494?

CVE-2025-62494 is a high-severity memory corruption vulnerability in QuickJS, published on 16 Oct 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.

  *  The code first checks if the left-hand operand is a string.

  *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).

  *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).

  *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.

This mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.

Weakness: CWE-704 (Incorrect Type Conversion or Cast)

## Which versions are affected by CVE-2025-62494?

It affects 1 product.


Products: Quickjs Project Quickjs.

## How do I fix CVE-2025-62494?

No fix has been published for CVE-2025-62494 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-62494 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-62494 exists.

## Other vulnerabilities in QuickJS

- [CVE-2025-62490](https://insights.sbomify.com/CVE-2025-62490/): Use-after-free in js_print_object in QuickJS (high 8.8)
- [CVE-2025-62491](https://insights.sbomify.com/CVE-2025-62491/): Use-after-free in js_std_promise_rejection_check in QuickJS (high 8.8)
- [CVE-2025-69654](https://insights.sbomify.com/CVE-2025-69654/): Denial of service in n/a (high 7.5)
- [CVE-2023-48183](https://insights.sbomify.com/CVE-2023-48183/): Null dereference in n/a (high 7.5)
- [CVE-2023-31922](https://insights.sbomify.com/CVE-2023-31922/): Denial of service in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-62494 and fix it if it is affected.

What it is: CVE-2025-62494 is a high-severity memory corruption vulnerability in QuickJS, published on 16 Oct 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-62494 exists.

Affected product: QuickJS. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2025-62494/ (Markdown: https://insights.sbomify.com/CVE-2025-62494/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-62494
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-62494
- OSV: https://osv.dev/vulnerability/CVE-2025-62494

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-62494/
Summaries are generated and may contain mistakes; the official description above is the record.