Vulnerability-Lookup

(CVE-2026-39834)

Vulnerability from cleanstart – Published: 2026-09-26 00:38 – Updated: 2026-09-25 10:23 – Source website

Summary

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 pa...

Details

Security vulnerability affects the loki package. 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.

Severity

9.8 (Critical)


                    
                      CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

URL

Type

	https://github.com/cleanstart-dev/cleanstart-secu…	ADVISORY
	https://osv.dev/vulnerability/CVE-2026-39834	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-39834	WEB

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "CleanStart",
        "name": "loki"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.7.1-r1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "credits": [],
  "database_specific": {},
  "details": "Security vulnerability affects the loki package. 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.",
  "id": "CLEANSTART-2026-UN89941",
  "modified": "2026-09-25T10:23:02Z",
  "published": "2026-09-26T00:38:00.610474Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/cleanstart-dev/cleanstart-security-advisories/tree/main/advisories/2026/CLEANSTART-2026-UN89941.json"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/CVE-2026-39834"
    },
    {
      "type": "WEB",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-39834"
    }
  ],
  "related": [],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "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 pa...",
  "upstream": [
    "CVE-2026-39834"
  ]
}

CVE-2026-39834 (GCVE-0-2026-39834)

Vulnerability from cvelistv5 – Published: 2026-05-22 02:31 – Updated: 2026-05-22 18:50

Title

Invoking infinite loop on large channel writes in golang.org/x/crypto/ssh

Summary

Severity

9.1 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-22 18:50 UTC

CWE

CWE-190 - Integer Overflow or Wraparound

Assigner

Go Google root

References

4 references

URL	Tags
https://go.dev/issue/79567
https://groups.google.com/g/golang-announce/c/a08…
https://go.dev/cl/781663
https://pkg.go.dev/vuln/GO-2026-5020

Impacted products

1 product

Vendor	Product	Version
golang.org/x/crypto	golang.org/x/crypto/ssh	Affected: 0 , < 0.52.0 (semver)

Credits

NCC Group Cryptography Services, sponsored by Teleport

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "cvssV3_1": {
              "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"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2026-39834",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-22T18:50:30.848292Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-22T18:50:51.339Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "collectionURL": "https://pkg.go.dev",
          "defaultStatus": "unaffected",
          "packageName": "golang.org/x/crypto/ssh",
          "product": "golang.org/x/crypto/ssh",
          "programRoutines": [
            {
              "name": "channel.WriteExtended"
            },
            {
              "name": "Dial"
            },
            {
              "name": "NewClientConn"
            },
            {
              "name": "NewServerConn"
            },
            {
              "name": "Session.CombinedOutput"
            },
            {
              "name": "Session.Output"
            },
            {
              "name": "Session.Run"
            },
            {
              "name": "Session.Shell"
            },
            {
              "name": "Session.Start"
            },
            {
              "name": "channel.Write"
            },
            {
              "name": "curve25519sha256.Client"
            },
            {
              "name": "curve25519sha256.Server"
            },
            {
              "name": "dhGEXSHA.Client"
            },
            {
              "name": "dhGEXSHA.Server"
            },
            {
              "name": "dhGroup.Client"
            },
            {
              "name": "dhGroup.Server"
            },
            {
              "name": "ecdh.Client"
            },
            {
              "name": "ecdh.Server"
            },
            {
              "name": "extChannel.Write"
            },
            {
              "name": "mlkem768WithCurve25519sha256.Client"
            },
            {
              "name": "mlkem768WithCurve25519sha256.Server"
            }
          ],
          "vendor": "golang.org/x/crypto",
          "versions": [
            {
              "lessThan": "0.52.0",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "value": "NCC Group Cryptography Services, sponsored by Teleport"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "description": "CWE-190: Integer Overflow or Wraparound",
              "lang": "en"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-22T02:31:27.540Z",
        "orgId": "1bb62c36-49e3-4200-9d77-64a1400537cc",
        "shortName": "Go"
      },
      "references": [
        {
          "url": "https://go.dev/issue/79567"
        },
        {
          "url": "https://groups.google.com/g/golang-announce/c/a082jnz-LvI"
        },
        {
          "url": "https://go.dev/cl/781663"
        },
        {
          "url": "https://pkg.go.dev/vuln/GO-2026-5020"
        }
      ],
      "title": "Invoking  infinite loop on large channel writes in golang.org/x/crypto/ssh"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "1bb62c36-49e3-4200-9d77-64a1400537cc",
    "assignerShortName": "Go",
    "cveId": "CVE-2026-39834",
    "datePublished": "2026-05-22T02:31:27.540Z",
    "dateReserved": "2026-04-07T18:13:03.529Z",
    "dateUpdated": "2026-05-22T18:50:51.339Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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(CVE-2026-39834)

CVE-2026-39834 (GCVE-0-2026-39834)

Tags

Sightings

Nomenclature

Related by attack behaviour