What is CVE-2026-27205?

CVE-2026-27205 is a medium-severity vulnerability in Pallets Flask, classified under Use of Cache Containing Sensitive Information. CVSS score: 4.3/10. Published 2026-02-21.

How severe is CVE-2026-27205?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Pallets Flask

CVE-2026-27205

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 Informa…

EPSS: 0.003 (26.7th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N.

Affected products

Pallets Flask — versions < 3.1.3
Palletsprojects Flask

Weakness classification (CWE)

CWE-524 — Use of Cache Containing Sensitive Information

References

security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)
security-advisories@github.com (Product, x_refsource_MISC, Release Notes)

Frequently asked questions

What is CVE-2026-27205?: CVE-2026-27205 is a medium-severity vulnerability in Pallets Flask, classified under Use of Cache Containing Sensitive Information. CVSS score: 4.3/10. Published 2026-02-21.
How severe is CVE-2026-27205?: Medium severity. CVSS v3 base score is 4.3 out of 10.