CVE-2025-62493
Heap out-of-bounds read in js_bigint_to_string1 in QuickJS
Published Oct 16, 2025
CVSS 4.0 · 5.9 Medium
EPSS < 1%
KEV · Not listed
Description
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:
$$ \\ \text{n\_digits} = (\text{n\_bits} + \text{log2\_radix} - 1) / \text{log2\_radix}$$
$$$$This formula is off-by-one in certain edge cases when calculating the necessary memory limbs. For instance, a 127-bit BigInt using radix 32 (where $\text{log2\_radix}=5$) is calculated to need $\text{n\_digits}=26$.
* The maximum number of bits actually stored is $\text{n\_bits}=127$, which requires only two 64-bit limbs ($\text{JS\_LIMB\_BITS}=64$).
* The conversion loop iterates $\text{n\_digits}=26$ times, attempting to read 5 bits in each iteration, totaling $26 \times 5 = 130$ bits.
* In the final iterations of the loop, the code attempts to read data that spans two limbs:
C
c = (r->tab[pos] >> shift) | (r->tab[pos + 1] << (JS_LIMB_BITS - shift));
* Since the BigInt was only allocated two limbs, the read operation for r->tab[pos + 1] becomes an Out-of-Bounds Read when pos points to the last valid limb (e.g., $pos=1$).
This vulnerability allows an attacker to cause the engine to read and process data from the memory immediately following the BigInt buffer. This can lead to Information Disclosure of sensitive data stored on the heap adjacent to the BigInt object.
* The function determines the number of characters (n_digits) needed for the string representation by calculating:
$$ \\ \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.
Affected Products
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CVE record
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NVD configurations
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Red Hat packages
No data
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OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| QuickJS | QuickJS | unaffected |
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No data.
| Vendor | Product | Versions |
|---|---|---|
| Quickjs-ng | Quickjs | — |
Remediation
Tracking
Advisories
Metrics
Attack Vector Adjacent Network
Attack Complexity High
Privileges Required Low
Attack Requirements Present
User Interaction Passive
Vulnerable System Confidentiality Impact High
Vulnerable System Integrity Impact Low
Vulnerable System Availability Impact Low
Subsequent System Confidentiality Impact High
Subsequent System Integrity Impact Low
Subsequent System Availability Impact Low
Attack Vector Adjacent Network
Attack Complexity Low
Privileges Required None
Scope Unchanged
Confidentiality Impact High
Integrity Impact None
Availability Impact None
User Interaction None
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.391% probability within 30 days)
Exploitation poc
Automatable no
Technical Impact partial
References
History
Oct 29, 2025 7:00 PM
First appearance in the feed. Affected versions updated. Affected vendors updated. Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Quickjs Project
Quickjs Project quickjs |
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| CPEs | cpe:2.3:a:quickjs_project:quickjs:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Quickjs Project
Quickjs Project quickjs |
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| Metrics |
cvssV3_1
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Oct 21, 2025 9:45 AM
First appearance in the feed. Affected vendors updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Quickjs-ng
Quickjs-ng quickjs |
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| Vendors & Products |
Quickjs-ng
Quickjs-ng quickjs |
Oct 16, 2025 6:15 PM
Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
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Oct 16, 2025 4:00 PM
Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | Heap out-of-bounds read in js_bigint_to_string1 in QuickJS | |
| Weaknesses | CWE-125 | |
| References |
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| Metrics |
cvssV4_0
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Subscriptions
Weaknesses
