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.
- 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
- None listed
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
Which versions are affected by CVE-2025-62494?
It affects 1 product.
Products include 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.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
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
Sources
Also known as DEBIAN-CVE-2025-62494, GHSA-7gcv-76g2-94qm, UBUNTU-CVE-2025-62494.