Vulnerability-Lookup

CVE-2026-86049 (GCVE-0-2026-86049)

Vulnerability from cvelistv5 – Published: 2026-09-17 20:28 – Updated: 2026-09-17 20:28

Title

Jupyter Server: 5xx request logging leaks token-bearing Referer header values

Summary

Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user's Jupyter Server permissions. This issue is fixed in version 2.21.0.

Severity

7.1 (High)


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

CWE

CWE-532 - Insertion of Sensitive Information into Log File

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/jupyter-server/jupyter_server/…	x_refsource_CONFIRM
https://github.com/jupyter-server/jupyter_server/…	x_refsource_MISC
https://github.com/jupyter-server/jupyter_server/…	x_refsource_MISC
https://github.com/jupyter-server/jupyter_server/…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
jupyter-server	jupyter_server	Affected: < 2.21.0	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "jupyter_server",
          "vendor": "jupyter-server",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.21.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user\u0027s Jupyter Server permissions. This issue is fixed in version 2.21.0."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.1,
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            "confidentialityImpact": "HIGH",
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      "problemTypes": [
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          "descriptions": [
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              "cweId": "CWE-532",
              "description": "CWE-532: Insertion of Sensitive Information into Log File",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-17T20:28:52.154Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2"
        },
        {
          "name": "https://github.com/jupyter-server/jupyter_server/pull/1681",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/jupyter-server/jupyter_server/pull/1681"
        },
        {
          "name": "https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717"
        },
        {
          "name": "https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0"
        }
      ],
      "source": {
        "advisory": "GHSA-c3mw-737p-c7g2",
        "discovery": "UNKNOWN"
      },
      "title": "Jupyter Server: 5xx request logging leaks token-bearing Referer header values"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-86049",
    "datePublished": "2026-09-17T20:28:52.154Z",
    "dateReserved": "2026-09-04T19:29:21.058Z",
    "dateUpdated": "2026-09-17T20:28:52.154Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "jupyter_server",
                "vendor": "jupyter-server",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c 2.21.0"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user\u0027s Jupyter Server permissions. This issue is fixed in version 2.21.0."
          }
        ],
        "id": "CVE-2026-86049",
        "lastModified": "2026-09-17T21:17:50.213",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 7.1,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "REQUIRED",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.2,
              "impactScore": 5.9,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-09-17T21:17:50.213",
        "references": [
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/jupyter-server/jupyter_server/pull/1681"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Received",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-532"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Primary"
          }
        ]
      }
    }
  }
}

FKIE_CVE-2026-86049

Vulnerability from fkie_nvd - Published: 2026-09-17 21:17 - Updated: 2026-09-17 21:17

Severity

7.1 (High) - CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717
	security-advisories@github.com	https://github.com/jupyter-server/jupyter_server/pull/1681
	security-advisories@github.com	https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0
	security-advisories@github.com	https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "jupyter_server",
          "vendor": "jupyter-server",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.21.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Jupyter Server is the backend for Jupyter web applications. Prior to version 2.21.0, the 5xx request logging path in jupyter_server/log.py copies the Referer header into a JSON header block without applying the token scrubbing used for the request URI. A request that returns HTTP 500 while the Referer contains a token-bearing URL can therefore write that token to server logs in plaintext. An attacker who can read those logs can recover the token and use the affected user\u0027s Jupyter Server permissions. This issue is fixed in version 2.21.0."
    }
  ],
  "id": "CVE-2026-86049",
  "lastModified": "2026-09-17T21:17:50.213",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.1,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.2,
        "impactScore": 5.9,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-09-17T21:17:50.213",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/jupyter-server/jupyter_server/pull/1681"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-532"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

GHSA-C3MW-737P-C7G2

Vulnerability from github – Published: 2026-09-17 20:28 – Updated: 2026-09-17 20:28

Summary

Jupyter Server: 5xx request logging leaks token-bearing Referer header values

Details

Summary

When a request returns a 500, jupyter_server/log.py logs a small JSON block of request headers.

The Referer header was copied into it as-is, so a token in the Referer URL ended up in the logs in plain text.

Impact

Anyone who can read the server logs can pick tokens out of these 500 entries. Tokens end up in the Referer during normal token-based login and launch flows.

Affected: all versions before 2.21.0.

PoC

Any malformed request that returns a 500 works:

curl -i -X POST \
  -H 'Content-Type: application/json' \
  -H 'Referer: http://127.0.0.1:8899/tree?token=REFERTOKEN' \
  --data '{"name":123}' \
  'http://127.0.0.1:8899/api/kernels?token=VALIDTOKEN'

The log shows the token twice, once raw and once redacted:

"Referer": "http://127.0.0.1:8899/tree?token=REFERTOKEN",
[E ... ServerApp] 500 POST /api/kernels?token=[secret] (...) referer=http://127.0.0.1:8899/tree?token=[secret]

Patches

Fixed in 2.21.0 by 5251352. Header values are now scrubbed before the block is logged. Upgrade to 2.21.0 or later.

Workarounds

Limit who can read the server logs. If you can, avoid flows that put the token in the URL.

Severity

7.1 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.20.0"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "jupyter_server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.21.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-86049"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-532"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-17T20:28:55Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\nWhen a request returns a 500, `jupyter_server/log.py` logs a small JSON block of request headers. \n\nThe Referer header was copied into it as-is, so a token in the Referer URL ended up in the logs in plain text.\n\n### Impact\n\nAnyone who can read the server logs can pick tokens out of these 500 entries. Tokens end up in the Referer during normal token-based login and launch flows.\n\nAffected: all versions before 2.21.0.\n\n### PoC\n\nAny malformed request that returns a 500 works:\n\n```bash\ncurl -i -X POST \\\n  -H \u0027Content-Type: application/json\u0027 \\\n  -H \u0027Referer: http://127.0.0.1:8899/tree?token=REFERTOKEN\u0027 \\\n  --data \u0027{\"name\":123}\u0027 \\\n  \u0027http://127.0.0.1:8899/api/kernels?token=VALIDTOKEN\u0027\n```\n\nThe log shows the token twice, once raw and once redacted:\n\n```\n\"Referer\": \"http://127.0.0.1:8899/tree?token=REFERTOKEN\",\n[E ... ServerApp] 500 POST /api/kernels?token=[secret] (...) referer=http://127.0.0.1:8899/tree?token=[secret]\n```\n\n### Patches\n\nFixed in 2.21.0 by 5251352. Header values are now scrubbed before the block is logged. Upgrade to 2.21.0 or later.\n\n### Workarounds\n\nLimit who can read the server logs. If you can, avoid flows that put the token in the URL.",
  "id": "GHSA-c3mw-737p-c7g2",
  "modified": "2026-09-17T20:28:55Z",
  "published": "2026-09-17T20:28:55Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-c3mw-737p-c7g2"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jupyter-server/jupyter_server/pull/1681"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jupyter-server/jupyter_server/commit/52513529af7096e622c00911b17627b266294717"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jupyter-server/jupyter_server"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jupyter-server/jupyter_server/releases/tag/v2.21.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Jupyter Server: 5xx request logging leaks token-bearing Referer header values"
}

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.

Detection rules are retrieved from Rulezet.

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.

Action not permitted

CVE-2026-86049 (GCVE-0-2026-86049)

FKIE_CVE-2026-86049

GHSA-C3MW-737P-C7G2

Summary

Impact

PoC

Patches

Workarounds

Tags

Sightings

Nomenclature

Related by attack behaviour