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CVE-2026-32240— Cap'n Proto: Integer overflow in KJ-HTTP chunk size

Quick assessment

Affected
capnproto capnproto
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.

capnproto是capnproto开源的一个 Proto 序列化/RPC 系统-核心工具和C++库 capnproto 1.4.0之前版本存在环境问题漏洞，该漏洞源于使用分块传输编码时，块大小解析值过大被截断为64位整数，可能导致HTTP请求或响应夹带。

AI Predicted 5.3 Difficulty: Theoretical EPSS 0.36% · P27

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-32240

Vulnerability Information
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Vulnerability Title
Cap'n Proto: Integer overflow in KJ-HTTP chunk size
Source: CVE Program / CVE List V5
Vulnerability Description
Cap'n Proto is a data interchange format and capability-based RPC system. Prior to 1.4.0, when using Transfer-Encoding: chunked, if a chunk's size parsed to a value of 2^64 or larger, it would be truncated to a 64-bit integer. In theory, this bug could enable HTTP request/response smuggling. This vulnerability is fixed in 1.4.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
数值截断错误
Source: CVE Program / CVE List V5
Vulnerability Title
capnproto 环境问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
capnproto是capnproto开源的一个 Proto 序列化/RPC 系统-核心工具和C++库 capnproto 1.4.0之前版本存在环境问题漏洞，该漏洞源于使用分块传输编码时，块大小解析值过大被截断为64位整数，可能导致HTTP请求或响应夹带。
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
capnproto capnproto < 1.4.0 -

II. Public POCs for CVE-2026-32240

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III. Intelligence Information for CVE-2026-32240

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Patches & Fixes for CVE-2026-32240 (2)

Vendor Advisories for CVE-2026-32240 (1)

Other References for CVE-2026-32240 (2)

IV. Related Vulnerabilities

Same product: capnproto
Same vendor: capnproto
Same weakness: CWE-197

V. Comments for CVE-2026-32240

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