7.5

CVE-2023-30861: Flask vulnerable to possible disclosure of permanent session cookie due to missing Vary: Cookie header

Modified
AliasesMGASA-2023-0193SUSE-SU-2023:2263-1SUSE-SU-2023:2264-1
Published 02-05-2023Last modified 13-02-2025

Vulnerability summary

CVE-2023-30861 is a high (CVSS 7.5) vulnerability in pallets flask. EPSS estimates a 1.25% chance of exploitation in the next 30 days, higher than 69.4% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 7.5 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 1% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
7.5/10
010
High · v3.1 (CVE.org)
EPSS score
1.25%
0%100%
Low · -0.01 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 3
RHSA-2023:3536RHSA-2023:3541RHSA-2023:3545

Timeline

  1. 02-05-2023
    PublishedVulnerability first disclosed.
  2. 13-02-2025
    Last modifiedVulnerability information updated.

Description

Flask is a lightweight WSGI web application framework. When all of the following conditions are met, a response containing data intended for one client may be cached and subsequently sent by the proxy to other clients. If the proxy also caches `Set-Cookie` headers, it may send one client's `session` cookie to other clients. The severity depends on the application's use of the session and the proxy's behavior regarding cookies. The risk depends on all these conditions being met. 1. The application must be hosted behind a caching proxy that does not strip cookies or ignore responses with cookies. 2. The application sets `session.permanent = True` 3. The application does not access or modify the session at any point during a request. 4. `SESSION_REFRESH_EACH_REQUEST` enabled (the default). 5. The application does not set a `Cache-Control` header to indicate that a page is private or should not be cached. This happens because vulnerable versions of Flask only set the `Vary: Cookie` header when the session is accessed or modified, not when it is refreshed (re-sent to update the expiration) without being accessed or modified. This issue has been fixed in versions 2.3.2 and 2.2.5.

CVSS metrics

7 scores · 6 sources · 2 versions

EPSS trend

Probability

1.25%

Chance of exploitation in the next 30 days

Percentile

69%

Versus all other CVEs

30-day change

Decrease -0.01 pp

From 1.26% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Suse19 products
  • python-Flask&distro=SUSE Enterprise Storage 7< 1.0.2-150100.6.3.1
  • python-Flask&distro=SUSE Enterprise Storage 7.1< 1.0.2-150100.6.3.1
  • python-Flask&distro=SUSE Linux Enterprise High Performance Computing 15 SP1-LTSS< 1.0.2-150100.6.3.1
  • python-Flask&distro=SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS< 1.0.2-150100.6.3.1
  • python-Flask&distro=SUSE Linux Enterprise High Performance Computing 15 SP3-ESPOS< 1.0.2-150100.6.3.1
Opensuse3 products
  • python-Flask&distro=openSUSE Leap 15.4< 1.0.4-150400.3.3.1
  • python-Flask&distro=openSUSE Leap 15.5< 1.0.4-150400.3.3.1
  • python-Flask&distro=openSUSE Tumbleweed< 3.1.3-3.1
Redhat2 products
  • python-flask< 1:1.1.2-6.el9ost | < 1:1.0.2-8.el8ost | < 1:0.10.1-7.el7_9
  • python3-flask< 1:1.1.2-6.el9ost | < 1:1.0.2-8.el8ost
Debian1 product
  • flask< 1.1.2-2+deb11u1 | < 1.0.2-3+deb10u1 | < 2.2.2-3
Mageia1 product
  • python-flask< 1.1.2-1.1.mga8
Pallets1 product
  • flask≥ 2.3.0, < 2.3.2 | < 2.2.5
Palletsprojects1 product
  • flask< 2.2.5 | ≥ 2.3.0, < 2.3.2
PyPI1 product
  • flask< 2.2.5 | < afd63b16170b7c047f5758eb910c416511e9c965 | ≥ 2.3.0, < 2.3.2
Ubuntu1 product
  • flask< 1.1.1-2ubuntu0.1 | < 2.0.1-2ubuntu1.1

9 vendors · 30 products

References

37 links
Show all 37 references