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Advisory record · GHSA-m2qf-hxjv-5gpq

Flask vulnerable to possible disclosure of permanent session cookie due to missing Vary: Cookie header

CVSS 7.5 HighEPSS 0.013 · 69th percentile

Published by the GitHub Advisory Database at 1 May 2023, 19:22 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
flaskPyPI>=2.3.0, <2.3.2 || <2.2.52.3.2, 2.2.5
Identifiers
GHSA-m2qf-hxjv-5gpq · CVE-2023-30861 · PYSEC-2023-62
Weakness (CWE)
CWE-539
Tags
Published
1 May 2023
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Flask versions from 2.2.5 (exclusive) up to 2.3.0 (exclusive), and from 2.3.0 up to 2.3.2 (exclusive), are affected. If a caching proxy sits in front of an application that sets session.permanent to True, never accesses the session during a request, keeps the default session refresh, and sets no private Cache-Control header, a response carrying one client's session cookie can be cached and sent to other clients. Upgrade to Flask 2.2.5 or 2.3.2. The source gives no workaround beyond upgrading.

Written 5 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
7.5 High 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.013, the 69th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:36 UTC First seen by agentprime
  2. 31 Oct 2026, 14:36 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.