CVE-2025-62493

What it is

A vulnerability exists in the QuickJS engine's BigInt string conversion logic (js_bigint_to_string1) due to an incorrect calculation of the required number of digits, which in turn leads to reading memory past the allocated BigInt structure. * The function determines the number of characters (n_digits) needed for the string representation by calculating: $$ \\ \text{n\_digits} = (\text{n\_bits} + \text{log2\_radix} - 1) / \text{log2\_radix}$$ $$$$This formula is off-by-one in certain edge cases when calculating the necessary memory limbs. For instance, a 127-bit BigInt using radix 32 (where $\text{log2\_radix}=5$) is calculated to need $\text{n\_digits}=26$. * The maximum number of bits actually stored is $\text{n\_bits}=127$, which requires only two 64-bit limbs ($\text{JS\_LIMB\_BITS}=64$). * The conversion loop iterates $\text{n\_digits}=26$ times, attempting to read 5 bits in each iteration, totaling $26 \times 5 = 130$ bits. * In the final iterations of the loop, the code attempts to read data that spans two limbs: C c = (r->tab[pos] >> shift) | (r->tab[pos + 1] << (JS_LIMB_BITS - shift)); * Since the BigInt was only allocated two limbs, the read operation for r->tab[pos + 1] becomes an Out-of-Bounds Read when pos points to the last valid limb (e.g., $pos=1$). This vulnerability allows an attacker to cause the engine to read and process data from the memory immediately following the BigInt buffer. This can lead to Information Disclosure of sensitive data stored on the heap adjacent to the BigInt object.

At a glance

Exploitability

Can be exploited from the same network segment with a low-privilege account, but needs a user to act. High risk of data exposure.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

No patch or advisory is linked yet. Look at mitigations or restrict exposure.

Timeline

1. 2025-10-16 16:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-19 16:10 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.4% in the next 30 days (EPSS).
• Severity: 5.9 MEDIUM (CVSS).
• Fix: none linked yet, which raises it.

Details

Published

2025-10-16 16:15 UTC

Last modified

2026-10-19 16:10 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-125 · Out-of-bounds read

Record status

Analyzed

Affected

• Quickjs Project Quickjs < 2025-09-13

Attack profile CVSS 4.0 · 5.9

Attack vector

Adjacent network

Complexity

High

Attack requirements

Present

Privileges needed

Low

User interaction

Passive

Confidentiality

High

Integrity

Low

Availability

Low

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2025-62493.md and follow it. Check whether this project is affected by CVE-2025-62493. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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