# CVE-2025-62496: Integer overflow in js_bigint_from_string in QuickJS

> An integer overflow in QuickJS BigInt parsing leads to heap out-of-bounds writes, potentially allowing code execution or crashes.

- **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-2025-62496, GHSA-p8pr-fr36-rgmq, UBUNTU-CVE-2025-62496

## What is CVE-2025-62496?

CVE-2025-62496 is a high-severity 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 vulnerability exists in the QuickJS engine's BigInt string parsing logic (js_bigint_from_string) when attempting to create a BigInt from a string with an excessively large number of digits.

The function calculates the necessary number of bits (n_bits) required to store the BigInt using the formula:

$$\text{n\_bits} = (\text{n\_digits} \times 27 + 7) / 8 \quad (\text{for radix 10})$$

  *  For large input strings (e.g., $79,536,432$ digits or more for base 10), the intermediate calculation $(\text{n\_digits} \times 27 + 7)$ exceeds the maximum value of a standard signed 32-bit integer, resulting in an Integer Overflow.

  *  The resulting n_bits value becomes unexpectedly small or even negative due to this wrap-around.

  *  This flawed n_bits is then used to compute n_limbs, the number of memory "limbs" needed for the BigInt object. Since n_bits is too small, the calculated n_limbs is also significantly underestimated.

  *  The function proceeds to allocate a JSBigInt object using this underestimated n_limbs.

  *  When the function later attempts to write the actual BigInt data into the allocated object, the small buffer size is quickly exceeded, leading to a Heap Out-of-Bounds Write as data is written past the end of the allocated r->tab array.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2025-62496?

It affects 1 product.


Products: Quickjs Project Quickjs.

## How do I fix CVE-2025-62496?

No fix has been published for CVE-2025-62496 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-62496 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-62496 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-2025-62496 and fix it if it is affected.

What it is: CVE-2025-62496 is a high-severity 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-2025-62496 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-2025-62496/ (Markdown: https://insights.sbomify.com/CVE-2025-62496/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-62496
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-62496
- OSV: https://osv.dev/vulnerability/CVE-2025-62496

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From sbomify Insights: https://insights.sbomify.com/CVE-2025-62496/
Summaries are generated and may contain mistakes; the official description above is the record.