CVE-2026-27205

CVE Enrichment

CVSS: 2.3 LOW
EPSS: 0.49%
EPSS Percentile: 40.46%
CISA KEV: Not listed

Description

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.

Technical Details

CVSS Version: 4.0
CNA / NVD Source: [email protected]
Published: 21-Feb-2026 13:17
Last Modified: 17-Jun-2026 17:26
EPSS Date: 2026-10-20
CWE: CWE-524

CVSS Vector


            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

Affected Products / Versions

palletsprojects / flask Source: NVD CPE · affected
Version / affected range: * · before (exclusive) 3.1.3
cpe:2.3:a:palletsprojects:flask:*:*:*:*:*:*:*:*

References

Last enrichment sync: 01-Nov-2026 20:19
Sources: NVD · FIRST EPSS · CISA KEV
Latest successful provider update; providers refresh independently.

Reported Context (1)

flask now sets “Vary: Cookie” when a session is accessed, CVE-2026-27205. Debian 13.7 Bundles 92 Security Advisories and Updates 106 Packages

CVE (19)

Products (18)

Note: Related entities, including threat actors, malware, CVEs, MITRE ATT&CK techniques, vendors, products, tools, countries, and industries, are shown when they appear in the same reporting. Their presence does not necessarily mean they were targeted, compromised, vulnerable, responsible for the activity, or directly involved in the incident.