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CVE-2026-42504— Quadratic complexity in WordDecoder.DecodeHeader in mime

Quick assessment

Affected
Go standard library mime
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.

Google Go是美国谷歌（Google）公司的一种静态强类型、编译型、并发型，并具有垃圾回收功能的编程语言。 Google Go存在安全漏洞，该漏洞源于解码包含许多无效编码词的恶意构造MIME标头可能消耗过多CPU。

AI Predicted 5.3 Difficulty: Easy EPSS 0.56% · P45

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
Go standard library mime < 1.25.11 affected
1.26.0-0< 1.26.4 affected
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I. Basic Information for CVE-2026-42504

Vulnerability Information
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Vulnerability Title
Quadratic complexity in WordDecoder.DecodeHeader in mime
Source: CVE Program / CVE List V5
Vulnerability Description
Decoding a maliciously-crafted MIME header containing many invalid encoded-words can consume excessive CPU.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Google Go 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Google Go是美国谷歌（Google）公司的一种静态强类型、编译型、并发型，并具有垃圾回收功能的编程语言。 Google Go存在安全漏洞，该漏洞源于解码包含许多无效编码词的恶意构造MIME标头可能消耗过多CPU。
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
Go standard library mime 0 ~ 1.25.11 -

II. Public POCs for CVE-2026-42504

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III. Intelligence Information for CVE-2026-42504

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Patches & Fixes for CVE-2026-42504 (1)

Vendor Advisories for CVE-2026-42504 (2)

Vendor Pages for CVE-2026-42504 (1)

Same Patch Batch · Go standard library · 2026-06-02 · 3 CVEs total

CVE-2026-42507 Arbitrary inputs are included in errors without any escaping in net/textproto
CVE-2026-27145 Inefficient candidate hostname parsing in crypto/x509

IV. Related Vulnerabilities

Same vendor: Go standard library

V. Comments for CVE-2026-42504

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