CVE-2025-62495 Affecting quickjs package, versions *

Note: Versions mentioned in the description apply only to the upstream quickjs package and not the quickjs package as distributed by Debian. See How to fix? for Debian:13 relevant fixed versions and status.

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);

• https://security-tracker.debian.org/tracker/CVE-2025-62495
• https://bellard.org/quickjs/Changelog
• https://issuetracker.google.com/434196926