CVE-2026-27205

Feb. 21, 2026, 6:17 a.m.

2.3
Low

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.

Product(s) Impacted

Vendor Product Versions
Pallets
  • Flask
  • <3.1.3

Weaknesses

Common security weaknesses mapped to this vulnerability.

CWE-524
Use of Cache Containing Sensitive Information
The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere.

*CPE(s)

Affected systems and software identified for this CVE.

Type Vendor Product Version Update Edition Language Software Edition Target Software Target Hardware Other Information
a pallets flask <3.1.3 / / / / / / /

References

https://github.com/pallets/flask/commit/089cb86dd22bff589a4eafb7ab8e42dc357623b4
https://github.com/pallets/flask/releases/tag/3.1.3
https://github.com/pallets/flask/security/advisories/GHSA-68rp-wp8r-4726

Tags

[email protected]
CWE-524
2026-02-21
CVE-2026-27205

CVSS Score

2.3 / 10

CVSS Data - 4.0

  • Attack Vector: NETWORK
  • Attack Complexity: LOW
  • Attack Requirements: PRESENT
  • Privileges Required: NONE
  • User Interaction: PASSIVE
  • Scope:
  • Confidentiality Impact: LOW
  • Integrity Impact: NONE
  • Availability Impact: NONE
  • Exploit Maturity: NOT_DEFINED

    • 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

    View Vector String

Timeline

Published: Feb. 21, 2026, 6:17 a.m.
Last Modified: Feb. 21, 2026, 6:17 a.m.

Status : Received

CVE has been recently published to the CVE List and has been received by the NVD.

More info

Source

[email protected]

*Disclaimer: Some vulnerabilities do not have an associated CPE. To enhance the data, we use AI to infer CPEs based on CVE details. This is an automated process and might not always be accurate.