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CVE-2026-32874— UltraJSON has a Memory Leak parsing large integers allows DoS

Quick assessment

Affected
ultrajson ultrajson
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

UltraJSON是UltraJSON开源的一个超快的 JSON 编码器和解码器，用纯 C 语言编写，并绑定了 Python 3.7+。 UltraJSON 5.11.0及之前版本存在安全漏洞，该漏洞源于解析大整数时存在内存泄漏，可能导致拒绝服务。

CVSS 7.5 · High EPSS 0.68% · P52

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
ultrajson ultrajson >= 5.4.0, < 5.12.0 affected
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I. Basic Information for CVE-2026-32874

Vulnerability Information
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Vulnerability Title
UltraJSON has a Memory Leak parsing large integers allows DoS
Source: CVE Program / CVE List V5
Vulnerability Description
UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.4.0 through 5.11.0 contain an accumulating memory leak in JSON parsing large (outside of the range [-2^63, 2^64 - 1]) integers. The leaked memory is a copy of the string form of the integer plus an additional NULL byte. The leak occurs irrespective of whether the integer parses successfully or is rejected due to having more than sys.get_int_max_str_digits() digits, meaning that any sized leak per malicious JSON can be achieved provided that there is no limit on the overall size of the payload. Any service that calls ujson.load()/ujson.loads()/ujson.decode() on untrusted inputs is affected and vulnerable to denial of service attacks. This issue has been fixed in version 5.12.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
在移除最后引用时对内存的释放不恰当(内存泄露)
Source: CVE Program / CVE List V5
Vulnerability Title
UltraJSON 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
UltraJSON是UltraJSON开源的一个超快的 JSON 编码器和解码器，用纯 C 语言编写，并绑定了 Python 3.7+。 UltraJSON 5.11.0及之前版本存在安全漏洞，该漏洞源于解析大整数时存在内存泄漏，可能导致拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ultrajson ultrajson >= 5.4.0, < 5.12.0 -

II. Public POCs for CVE-2026-32874

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III. Intelligence Information for CVE-2026-32874

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Patches & Fixes for CVE-2026-32874 (1)

Vendor Advisories for CVE-2026-32874 (1)

Vendor Pages for CVE-2026-32874 (1)

IV. Related Vulnerabilities

Same product: ultrajson
Same vendor: ultrajson
Same weakness: CWE-401

V. Comments for CVE-2026-32874

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