Vulnerability-Lookup

OESA-2026-2136 (CVE-2026-27205)

Vulnerability from osv_openeuler – Published: 2026-05-03 11:11 – Updated: 2026-08-06 11:11 – Source website

Summary

python-flask security update

Details

Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. It began as a simple wrapper around Werkzeug and Jinja and has become one of the most popular Python web application frameworks.

Security Fix(es):

Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.(CVE-2026-27205)

Severity

2.3 (Low)


                    
                      CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

References

URL

Type

	https://www.openeuler.org/zh/security/security-bu…	ADVISORY
	https://nvd.nist.gov/vuln/detail/CVE-2026-27205	ADVISORY

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "noarch": [
          "python3-flask-2.2.5-2.oe2403.noarch.rpm"
        ],
        "src": [
          "python-flask-2.2.5-2.oe2403.src.rpm"
        ]
      },
      "package": {
        "ecosystem": "openEuler:24.03-LTS",
        "name": "python-flask",
        "purl": "pkg:rpm/openEuler/python-flask\u0026distro=openEuler-24.03-LTS"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.2.5-2.oe2403"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "severity": "Low"
  },
  "details": "Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. It began as a simple wrapper around Werkzeug and Jinja and has become one of the most popular Python web application frameworks.\r\n\r\nSecurity Fix(es):\n\nFlask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn\u0026apos;t ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.(CVE-2026-27205)",
  "id": "OESA-2026-2136",
  "modified": "2026-08-06T11:11:07Z",
  "published": "2026-05-03T11:11:07Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-2136"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27205"
    }
  ],
  "schema_version": "1.7.2",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ],
  "summary": "python-flask security update",
  "upstream": [
    "CVE-2026-27205"
  ]
}

CVE-2026-27205 (GCVE-0-2026-27205)

Vulnerability from cvelistv5 – Published: 2026-02-21 05:21 – Updated: 2026-02-24 19:03

Title

Flask session does not add `Vary: Cookie` header when accessed in some ways

Summary

Severity

2.3 (Low)


                        
                          CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-02-24 19:02 UTC

CWE

CWE-524 - Use of Cache Containing Sensitive Information

Assigner

GitHub_M mitre root Scorecard

References

3 references

URL	Tags
https://github.com/pallets/flask/security/advisor…	x_refsource_CONFIRM
https://github.com/pallets/flask/commit/089cb86dd…	x_refsource_MISC
https://github.com/pallets/flask/releases/tag/3.1.3	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
pallets	flask	Affected: < 3.1.3

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-27205",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-02-24T19:02:52.515600Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-02-24T19:03:11.374Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "flask",
          "vendor": "pallets",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 3.1.3"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn\u0027t ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 2.3,
            "baseSeverity": "LOW",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "PASSIVE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "LOW",
            "vulnIntegrityImpact": "NONE"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-524",
              "description": "CWE-524: Use of Cache Containing Sensitive Information",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-02-21T05:21:17.214Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/pallets/flask/security/advisories/GHSA-68rp-wp8r-4726",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/pallets/flask/security/advisories/GHSA-68rp-wp8r-4726"
        },
        {
          "name": "https://github.com/pallets/flask/commit/089cb86dd22bff589a4eafb7ab8e42dc357623b4",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pallets/flask/commit/089cb86dd22bff589a4eafb7ab8e42dc357623b4"
        },
        {
          "name": "https://github.com/pallets/flask/releases/tag/3.1.3",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pallets/flask/releases/tag/3.1.3"
        }
      ],
      "source": {
        "advisory": "GHSA-68rp-wp8r-4726",
        "discovery": "UNKNOWN"
      },
      "title": "Flask session does not add `Vary: Cookie` header when accessed in some ways"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-27205",
    "datePublished": "2026-02-21T05:21:17.214Z",
    "dateReserved": "2026-02-18T19:47:02.155Z",
    "dateUpdated": "2026-02-24T19:03:11.374Z",
    "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.

Action not permitted

OESA-2026-2136 (CVE-2026-27205)

CVE-2026-27205 (GCVE-0-2026-27205)

Tags

Sightings

Nomenclature

Related by attack behaviour