CVE-2023-30861
HIGHDescription
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.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Exploit Intelligence
Moderate risk: more likely to be exploited than 67% of all known CVEs.
References
Related Vulnerabilities
Other CWE-539 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2021-27463 | Medium | 5.3 | 0.9% | - | - |
| CVE-2026-35192 | Medium | 6.5 | 0.5% | - | Fix |
| CVE-2025-27673 | Critical | 9.1 | 0.5% | - | Fix |
| CVE-2024-39275 | High | 8.0 | 0.4% | - | Fix |
| CVE-2025-52633 | Low | 3.1 | 0.2% | - | - |
| CVE-2026-24318 | Medium | 4.2 | 0.2% | - | - |
Common questions
How do I fix CVE-2023-30861?
Published advisories record a fix for 135 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2023-30861 being actively exploited?
Not that we know of. CVE-2023-30861 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.3% is the estimated probability that it will be exploited in the next 30 days. That is higher than 67% of all scored CVEs.
How severe is CVE-2023-30861?
CVE-2023-30861 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2023-30861 affect?
Published advisories record a fix for flask (Debian), NetworkManager (Rocky), NetworkManager (Red Hat / RHEL), NetworkManager-adsl (Rocky), and 131 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.