CVE-2026-39820

Description

Well-crafted inputs reaching ParseAddress, ParseAddressList, and ParseDate were able to trigger excessive CPU exhaustion and memory allocations.

Overview

State: PUBLISHED
Assigner (CNA): Go
CVSS severity: high
CVSS score: 7.5 / 10
CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Effective score: 7.5 / 10 HIGH source: CNA overview
MSRC score: 7.5 / 10 HIGH MS rating: Important
CWE(s): CWE-407: Inefficient Algorithmic Complexity
Reserved: 2026-04-07
Published: 2026-05-07 19:41 UTC
Last updated: 2026-05-08 14:27 UTC
Source: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/39xxx/CVE-2026-39820.json
Linked Threat: CVE-2026-39820 — CVE-2026-39820

NVD triage scoring NVD CVE 2.0

Layer NVD adds on top of the CNA's CVE record — published / last-modified timestamps, exploitability / impact subscores, and the FIRST.org EPSS probability that this CVE will be exploited in the wild in the next 30 days.

NVD published: 2026-05-07 20:16:43 UTC
NVD last modified: 2026-05-13 15:10:58 UTC
NVD CVSS v3.1: 7.5 / 10 HIGH source: nvd@nist.gov
NVD CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploitability subscore: 3.9 / 10
Impact subscore: 3.6 / 10
EPSS score: 0.0005 (probability of exploitation in next 30 days)
EPSS percentile: 16.83% vs all CVEs — higher = more likely to be exploited, as of 2026-05-24

NVD-assigned CWE(s): CWE-770 (differs from the CNA list above)

European Union Vulnerability Database ENISA EUVD

ENISA's official EU repository for curated vulnerability intelligence. Carries a separate identifier (EUVD-YYYY-NNNN) and frequently exposes an earlier-published description + CVSS than NVD does.

EUVD ID: EUVD-2026-28423
Assigner: Go
Published: May 7, 2026, 7:41:19 PM
Updated: Jul 29, 2026, 12:04:43 PM
EUVD base score (CVSS 3.1): 7.5 / 10
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EUVD-reported EPSS: 0.7800
Vendors: Go standard library
Products: net/mail (1.26.0-0 <1.26.3)

net/mail (0 <1.25.10)

ENISA description: Well-crafted inputs reaching ParseAddress, ParseAddressList, and ParseDate were able to trigger excessive CPU exhaustion and memory allocations.

EUVD references (4)

Microsoft Security Response Center MSRC

Microsoft's vendor-authoritative record from the Security Update Guide — its own CVSS score, impact, severity rating, exploit assessment, and KB-article fixes. Refreshed 2026-08-12 01:09 UTC (source: CVRF).

MS severity: Important
MS CVSS base score: 7.5 / 10 (temporal 7.5)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Release: 2026-May

Affected products (1)

Vendor	Product	Versions	Platforms
Go standard library	net/mail	`0` (affected), `1.26.0-0` (affected)	—

Affected products — CPE 2.3 (1) NVD

NVD's normalized CPE 2.3 matchers, used by vendor tools (vulnerability scanners, asset managers) for automated detection. Compare with the CNA's free-text "Affected products" section above.

cpe:2.3:a:golang:go:*:*:*:*:*:*:*:*

Vendor references (4)

References embedded in the original CVE record by the assigning CNA.

Web references (12)

DuckDuckGo results ranked by threat-intel / vendor advisory domains. Generated by the 🔎 Find references (web) button above — same flow as the Remediations search.

MSRC update guide: CVE-2026-39820 msrc
https://attackerkb.com/topics/CVE-2026-39820 rapid7:attackerkb.com
https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-28423 rapid7:euvd.enisa.europa.eu
http://cwe.mitre.org/data/definitions/770.html rapid7:cwe.mitre.org
https://security.alpinelinux.org/vuln/CVE-2026-39820 rapid7:security.alpinelinux.org
https://groups.google.com/g/golang-announce/c/qcCIEXso47M tenable:groups.google.com
https://go.dev/cl/759940 tenable:go.dev
https://nvd.nist.gov/vuln/detail/CVE-2026-39820 tenable:nvd.nist.gov
https://pkg.go.dev/vuln/GO-2026-4986 tenable:pkg.go.dev
https://www.first.org/epss/ tenable:www.first.org
https://www.cve.org/CVERecord?id=CVE-2026-39820 tenable:www.cve.org
https://go.dev/issue/78566 tenable:go.dev

NVD-tagged references (4)

Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.

https://go.dev/cl/759940 security@golang.org Patch
https://go.dev/issue/78566 security@golang.org Issue Tracking
https://groups.google.com/g/golang-announce/c/qcCIEXso47M security@golang.org Issue TrackingMailing List
https://pkg.go.dev/vuln/GO-2026-4986 security@golang.org Vendor Advisory

Remediations (14)

Remediations are stored against the linked Threat row; the list below is deduplicated across both pages.

Microsoft Patch Tuesday April 2026 - 168 Vulnerabilities Fixed ...

web:cybersecuritynews.com

Microsoft has released its April 2026 Patch Tuesday security update, addressing 168 vulnerabilities across its product portfolio including one actively exploited zero-day and one publicly disclosed flaw that organizations must prioritize immediately.

2026-05-23 21:51 UTC
Patch Tuesday, May 2026 Edition - Krebs on Security

web:krebsonsecurity.com

Microsoft expects that exploitation is more likely. May's Patch Tuesday is a welcome respite from April, which saw Microsoft fix a near-record 167 security flaws.

2026-05-23 21:51 UTC
Nvd - Cve-2026-39820

web:nvd.nist.gov

Official websites use .gov A .gov website belongs to an official government organization in the United States.

2026-05-23 21:51 UTC
Security Update Guide - Microsoft

web:portal.msrc.microsoft.com

The Security Update Guide provides information on the latest Microsoft security updates, helping users understand and address potential vulnerabilities effectively.

2026-05-23 21:51 UTC
CVE-2026-39820 - security-tracker.debian.org

web:security-tracker.debian.org

Vulnerable and fixed packages The table below lists information on source packages.

2026-05-23 21:51 UTC
Critical Patches Issued for Microsoft Products, April 14, 2026

web:www.cisecurity.org

<p>Multiple vulnerabilities have been discovered in Microsoft products, the most severe of which could allow for remote code execution. Successful exploitation of the most severe of these vulnerabilities could result in an attacker gaining the same privileges as the logged-on user. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or ...

2026-05-23 21:51 UTC
April 2026 Patch Tuesday: Updates and Analysis | CrowdStrike

web:www.crowdstrike.com

Microsoft's April 2026 Patch Tuesday addresses 164 CVEs , featuring 8 Critical vulnerabilities, one exploited zero-day, and one disclosed zero-day.

2026-05-23 21:51 UTC
Oracle Critical Patch Update Advisory - April 2026

web:www.oracle.com

This Critical Patch Update contains 481 new security patches across the product families listed below. Please note that an MOS note summarizing the content of this Critical Patch Update and other Oracle Software Security Assurance activities is located at April 2026 Critical Patch Update: Executive Summary and Analysis.

2026-05-23 21:51 UTC
CVE-2026-39820 Common Vulnerabilities and Exposures | SUSE

web:www.suse.com

Secure your Linux systems from CVE-2026-39820 . Stay ahead of potential threats with the latest security updates from SUSE.

2026-05-23 21:51 UTC
CVE-2026-39820 - High Vulnerability - TheHackerWire

web:www.thehackerwire.com

CVE-2026-39820 is a High severity vulnerability (CVSS 7.5). Well-crafted inputs reaching ParseAddress, ParseAddressList, and ParseDate were able to trigger excessive CPU exhaustion and memory allocations.

2026-05-23 21:51 UTC
CISA Warns of Exploited Microsoft Defender 0-Day Flaws

web:cyberpress.org

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has added two actively exploited Microsoft Defender vulnerabilities to its Known Exploited Vulnerabilities (KEV) catalog, issuing an urgent remediation directive for federal agencies with a due date of June 3, 2026 .

2026-05-26 02:46 UTC
Security Update Guide - Microsoft

web:msrc.microsoft.com

The Microsoft Security Response Center (MSRC) investigates all reports of security vulnerabilities affecting Microsoft products and services, and provides the information here as part of the ongoing effort to help you manage security risks and help keep your systems protected.

2026-05-26 02:46 UTC
February's Patch Tuesday release fixes 59 flaws ... - Computerworld

web:www.computerworld.com

Each month, the team at Readiness analyzes the latest Patch Tuesday updates from Microsoft and provides detailed, actionable testing guidance. The company's Patch Tuesday release for February ...

2026-05-26 02:46 UTC
Patch Tuesday May 2026: Security Updates & CVE Analysis

web:zecurit.com

Get the complete breakdown of Microsoft's May 2026 Patch Tuesday. We analyze the latest security updates and all critical CVEs .

2026-05-26 02:46 UTC

AI Forensic Analysis

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Raw JSON

The full cvelistV5 record. Download as CVE-2026-39820.json.

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      "title": "Quadratic string concatentation in consumeComment in net/mail"
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