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CVE-2026-39820— Quadratic string concatentation in consumeComment in net/mail

Quick assessment

Affected
Go standard library net/mail
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，该漏洞源于精心构造的输入可能触发过度的CPU消耗和内存分配。

AI Predicted 7.5 Difficulty: Easy EPSS 0.78% · P54

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 2

VendorProduct Version RangeStatus
Go standard library net/mail < 1.25.10 affected
1.26.0-0< 1.26.3 affected
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I. Basic Information for CVE-2026-39820

Vulnerability Information
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Vulnerability Title
Quadratic string concatentation in consumeComment in net/mail
Source: CVE Program / CVE List V5
Vulnerability Description
Well-crafted inputs reaching ParseAddress, ParseAddressList, and ParseDate were able to trigger excessive CPU exhaustion and memory allocations.
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，该漏洞源于精心构造的输入可能触发过度的CPU消耗和内存分配。
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 net/mail 0 ~ 1.25.10 -

II. Public POCs for CVE-2026-39820

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III. Intelligence Information for CVE-2026-39820

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Patches & Fixes for CVE-2026-39820 (1)

Vendor Advisories for CVE-2026-39820 (1)

Vendor Pages for CVE-2026-39820 (1)

Other References for CVE-2026-39820 (1)

Same Patch Batch · Go standard library · 2026-05-07 · 7 CVEs total

CVE-2026-42499 Quadratic string concatenation in consumePhrase in net/mail
CVE-2026-39836 Panic in Dial and LookupPort when handling NUL byte on Windows in net
CVE-2026-39826 Escaper bypass leads to XSS in html/template
CVE-2026-39825 ReverseProxy forwards queries with more than urlmaxqueryparams parameters in net/http/http
CVE-2026-39823 Bypass of meta content URL escaping causes XSS in html/template
CVE-2026-33811 Crash when handling long CNAME response in net

IV. Related Vulnerabilities

Same product: net/mail
Same vendor: Go standard library

V. Comments for CVE-2026-39820

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