CVE-2026-39834

Description

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.

Overview

State: PUBLISHED
Assigner (CNA): Go
CVSS severity: critical
CVSS score: 9.1 / 10
CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Effective score: 9.1 / 10 CRITICAL source: CNA overview
MSRC score: 9.1 / 10 CRITICAL MS rating: Important
CWE(s): CWE-190: Integer Overflow or Wraparound
Reserved: 2026-04-07
Published: 2026-05-22 02:31 UTC
Last updated: 2026-05-22 18:50 UTC
Source: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/39xxx/CVE-2026-39834.json
Linked Threat: CVE-2026-39834 — CVE-2026-39834

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: 2026-05-22 04:16:24 UTC
NVD last modified: 2026-05-22 04:16:24 UTC
EPSS score: 0.0004 (probability of exploitation in next 30 days)
EPSS percentile: 12.73% vs all CVEs — higher = more likely to be exploited, as of 2026-05-24

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-2026-31400
Assigner: Go
Published: May 22, 2026, 2:31:27 AM
Updated: May 22, 2026, 6:50:51 PM
EUVD base score (CVSS 3.1): 9.1 / 10
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
EUVD-reported EPSS: 0.0500
Vendors: golang.org/x/crypto
Products: golang.org/x/crypto/ssh (0 <0.52.0)

ENISA description: When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.

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: 9.1 / 10 (temporal 8.3)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H/E:U
Release: 2026-May

Microsoft remediations / KB articles (2)

CBL-Mariner Releases — Vendor Fix / Security Update (fixed build 1.12.15-8)
https://learn.microsoft.com/en-us/azure/azure-linux/tutorial-azure-linux-upgrade — None Available / CBL-Mariner Releases

Affected products (1)

Vendor	Product	Versions	Platforms
golang.org/x/crypto	golang.org/x/crypto/ssh	`0` (affected)	—

Vendor references (4)

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

Web references (9)

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

None Available msrc
MSRC update guide: CVE-2026-39834 msrc
https://www.first.org/epss/ tenable:www.first.org
https://groups.google.com/g/golang-announce/c/a082jnz-LvI tenable:groups.google.com
https://go.dev/issue/79567 tenable:go.dev
https://nvd.nist.gov/vuln/detail/CVE-2026-39834 tenable:nvd.nist.gov
https://pkg.go.dev/vuln/GO-2026-5020 tenable:pkg.go.dev
https://www.cve.org/CVERecord?id=CVE-2026-39834 tenable:www.cve.org
https://go.dev/cl/781663 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/781663 security@golang.org
https://go.dev/issue/79567 security@golang.org
https://groups.google.com/g/golang-announce/c/a082jnz-LvI security@golang.org
https://pkg.go.dev/vuln/GO-2026-5020 security@golang.org

Remediations (10)

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

Security Advisory Bulletin 064 | Ubiquiti Community

web:community.ui.com

Published: May 21, 2026 Updated: May 22, 2026 Version: 1.1 Revision: 1.1 Summary 1 of 5 A malicious actor with access to the network and high privileges could exploit an Improper Input Validation vulnerability found in UniFi OS devices to execute a Command Injection. Affected Products: UniFi OS Server (Version 5.0.6 and earlier) Mitigation : Update your UniFi OS Server to Version 5.0.8 or later ...

2026-05-26 03:00 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 03:00 UTC
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.

2026-05-26 03:00 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.

2026-05-26 03:00 UTC
"Error 1328. Error applying patch to file C:\Config.Msi ... - Autodesk

web:www.autodesk.com

When installing a Revit update, the following message appears: Error 1328.Error applying patch to file C:\Config.Msi\xxx.tmp. It has probably been updated by other means, and can no longer be modified by this patch .

2026-05-26 03:00 UTC
GitHub fixes RCE flaw that gave access to millions of private repos

web:www.bleepingcomputer.com

In early March, GitHub patched a critical remote code execution vulnerability ( CVE - 2026 -3854) that could have allowed attackers to access millions of private repositories.

2026-05-26 03:00 UTC
National Vulnerability Database | NIST

web:www.nist.gov

NIST maintains the National Vulnerability Database (NVD), a repository of information on software and hardware flaws that can compromise computer security. This is a key piece of the nation's cybersecurity infrastructure.

2026-05-26 03:00 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.

2026-05-26 03:00 UTC
CVE-2026-39813: FortiSandbox Path Traversal Vulnerability

web:www.sentinelone.com

CVE - 2026 -39813 is a path traversal vulnerability in Fortinet FortiSandbox. Learn about its impact, affected versions, and mitigation methods.

2026-05-26 03:00 UTC
GitHub RCE Vulnerability: CVE-2026-3854 Breakdown | Wiz Blog

web:www.wiz.io

Securing GitHub: Wiz Research uncovers Remote Code Execution in GitHub.com and GitHub Enterprise Server ( CVE - 2026 -3854) Details on CVE - 2026 -3854: A critical flaw in GitHub's internal git infrastructure enabling RCE on GitHub.com and GitHub Enterprise Server.

2026-05-26 03:00 UTC

AI Forensic Analysis

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Raw JSON

The full cvelistV5 record. Download as CVE-2026-39834.json.

{
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              "attackComplexity": "LOW",
              "attackVector": "NETWORK",
              "availabilityImpact": "HIGH",
              "baseScore": 9.1,
              "baseSeverity": "CRITICAL",
              "confidentialityImpact": "NONE",
              "integrityImpact": "HIGH",
              "privilegesRequired": "NONE",
              "scope": "UNCHANGED",
              "userInteraction": "NONE",
              "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H",
              "version": "3.1"
            }
          },
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                "options": [
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                  },
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                    "Automatable": "yes"
                  },
                  {
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                  }
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                "role": "CISA Coordinator",
                "timestamp": "2026-05-22T18:50:30.848292Z",
                "version": "2.0.3"
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    "cna": {
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          "defaultStatus": "unaffected",
          "packageName": "golang.org/x/crypto/ssh",
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            {
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            {
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            {
              "name": "mlkem768WithCurve25519sha256.Client"
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            }
          ],
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          "versions": [
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          ]
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      "credits": [
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          "lang": "en",
          "value": "NCC Group Cryptography Services, sponsored by Teleport"
        }
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          "lang": "en",
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        },
        {
          "url": "https://pkg.go.dev/vuln/GO-2026-5020"
        }
      ],
      "title": "Invoking  infinite loop on large channel writes in golang.org/x/crypto/ssh"
    }
  },
  "cveMetadata": {
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    "dateReserved": "2026-04-07T18:13:03.529Z",
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