CVE-2026-27205

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Source
https://cve.org/CVERecord?id=CVE-2026-27205
Import Source
https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-27205.json
JSON Data
https://api.test.osv.dev/v1/vulns/CVE-2026-27205
Aliases
Downstream
Related
Published
2026-02-21T05:21:17.214Z
Modified
2026-02-22T01:47:37.807853Z
Severity
  • 2.3 (Low) CVSS_V4 - 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 CVSS Calculator
Summary
Flask session does not add `Vary: Cookie` header when accessed in some ways
Details

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.

Database specific 
{
    "cwe_ids": [
        "CWE-524"
    ],
    "cna_assigner": "GitHub_M",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27205.json"
}
References

Affected packages

Git / github.com/pallets/flask

Affected ranges

Type
GIT
Repo
https://github.com/pallets/flask
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
22d924701a6ae2e4cd01e9a15bbaf3946094af65

Affected versions

0.*
0.1
0.10
0.10.1
0.11
0.11.1
0.12
0.12.1
0.12.2
0.12.3
0.12.4
0.12.5
0.12.x
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.8.1
0.9
1.*
1.0
1.0.1
1.0.2
1.0.3
1.0.4
1.0.x
1.1.0
1.1.1
1.1.2
1.1.3
1.1.4
1.1.x
2.*
2.0.0
2.0.0rc1
2.0.0rc2
2.0.1
2.0.2
2.0.3
2.1.0
2.1.1
2.1.2
2.1.3
2.1.x
2.2.0
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.x
2.3.0
2.3.1
2.3.2
2.3.3
2.3.x
3.*
3.0.1
3.0.2
3.0.3
3.1.0
3.1.1
3.1.2

Database specific

source 
"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-27205.json"