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.
- 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-2025-62495?
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
Which versions are affected by CVE-2025-62495?
It affects 1 product.
Products include 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
Sources
Also known as DEBIAN-CVE-2025-62495, GHSA-g8rq-rjvv-4hcc, UBUNTU-CVE-2025-62495.