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CVE-2026-32875— UltraJSON has an integer overflow handling large indent leads to buffer overflow or infinite loop

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，该漏洞源于处理大缩进时存在缓冲区溢出或无限循环，可能导致拒绝服务。

CVSS 7.5 · High EPSS 0.77% · P55

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
ultrajson ultrajson >= 5.1.0, < 5.12.0 affected
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I. Basic Information for CVE-2026-32875

Vulnerability Information
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Vulnerability Title
UltraJSON has an integer overflow handling large indent leads to buffer overflow or infinite loop
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 5.10 through 5.11.0 are vulnerable to buffer overflow or infinite loop through large indent handling. ujson.dumps() crashes the Python interpreter (segmentation fault) when the product of the indent parameter and the nested depth of the input exceeds INT32_MAX. It can also get stuck in an infinite loop if the indent is a large negative number. Both are caused by an integer overflow/underflow whilst calculating how much memory to reserve for indentation. And both can be used to achieve denial of service. To be vulnerable, a service must call ujson.dump()/ujson.dumps()/ujson.encode() whilst giving untrusted users control over the indent parameter and not restrict that indentation to reasonably small non-negative values. A service may also be vulnerable to the infinite loop if it uses a fixed negative indent. An underflow always occurs for any negative indent when the input data is at least one level nested but, for small negative indents, the underflow is usually accidentally rectified by another overflow. 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
整数溢出或超界折返
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，该漏洞源于处理大缩进时存在缓冲区溢出或无限循环，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 >= 5.1.0, < 5.12.0 -

II. Public POCs for CVE-2026-32875

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III. Intelligence Information for CVE-2026-32875

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Patches & Fixes for CVE-2026-32875 (1)

Vendor Advisories for CVE-2026-32875 (1)

Proof of Concept for CVE-2026-32875 (1)

IV. Related Vulnerabilities

Same product: ultrajson
Same vendor: ultrajson
Same weakness: CWE-190

V. Comments for CVE-2026-32875

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