# CVE-2025-62495: Type confusion in string addition in QuickJS

> An integer overflow in QuickJS regex engine allows out-of-bounds writes, potentially enabling remote code execution via crafted regular expressions.

- **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-2025-62495, GHSA-g8rq-rjvv-4hcc, UBUNTU-CVE-2025-62495

## What is CVE-2025-62495?

CVE-2025-62495 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

An integer overflow vulnerability exists in the QuickJS regular expression engine (libregexp) due to an inconsistent representation of the bytecode buffer size.

  *  The regular expression bytecode is stored in a DynBuf structure, which correctly uses a $\text{size}\_\text{t}$ (an unsigned type, typically 64-bit) for its size member.

  *  However, several functions, such as re_emit_op_u32 and other internal parsing routines, incorrectly cast or store this DynBuf $\text{size}\_\text{t}$ value into a signed int (typically 32-bit).

  *  When a large or complex regular expression (such as those generated by a recursive pattern in a Proof-of-Concept) causes the bytecode size to exceed $2^{31}$ bytes (the maximum positive value for a signed 32-bit integer), the size value wraps around, resulting in a negative integer when stored in the int variable (Integer Overflow).

  *  This negative value is subsequently used in offset calculations. For example, within functions like re_parse_disjunction, the negative size is used to compute an offset (pos) for patching a jump instruction.

  *  This negative offset is then incorrectly added to the buffer pointer (s->byte\_code.buf + pos), leading to an out-of-bounds write on the first line of the snippet below:

put_u32(s->byte_code.buf + pos, len);

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2025-62495?

It affects 1 product.


Products: Quickjs Project Quickjs.

## How do I fix CVE-2025-62495?

No fix has been published for CVE-2025-62495 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-62495 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-62495 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-2025-62495 and fix it if it is affected.

What it is: CVE-2025-62495 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-2025-62495 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-2025-62495/ (Markdown: https://insights.sbomify.com/CVE-2025-62495/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-62495
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-62495
- OSV: https://osv.dev/vulnerability/CVE-2025-62495

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From sbomify Insights: https://insights.sbomify.com/CVE-2025-62495/
Summaries are generated and may contain mistakes; the official description above is the record.