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CVE details

CVE-2025-62493

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.

Score
5.9 medium
Published
2025-10-16
Links
NVD · cve.org

Affected ports (1)

PortPackageVersionStatusMaintainer
lang/quickjs-ngquickjs-ng0.17.0unaddressedosa@FreeBSD.org

Template for a VuXML entry

Range taken from the CVE record, check it before committing. make newentry in security/vuxml creates the vid.

  <vuln vid="FIXME (make newentry)">
    <topic>FIXME -- FIXME</topic>
    <affects>
      <package>
	<name>quickjs-ng</name>
	<range><lt>2025-09-13</lt></range>
      </package>
    </affects>
    <description>
      <body xmlns="http://www.w3.org/1999/xhtml">
	<p>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.</p>
      </body>
    </description>
    <references>
      <cvename>CVE-2025-62493</cvename>
      <url>https://nvd.nist.gov/vuln/detail/CVE-2025-62493</url>
    </references>
    <dates>
      <discovery>2025-10-16</discovery>
      <entry>2026-10-25</entry>
    </dates>
  </vuln>