# CVE-2025-47278: PYSEC-2026-1377 - Flask uses fallback key instead of current signing key

Source: https://junglewise.ai/threats/cve-2025-47278-flask-uses-fallback-key-instead-of-current-signing-key  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-07  
License: CC BY 4.0 with a link back

CVE-2025-47278 · Severity: medium · CVSS 4 · Published 2026-07-07

Flask uses fallback key instead of current signing key

Technologies: [flask (PyPI)](https://junglewise.ai/threats/technologies/flask). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2025-47278 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-47278 being exploited in the wild.

**How severe is CVE-2025-47278?** Medium severity, with a CVSS score of 4, published 7 July 2026.

**Which products and versions are affected?** flask (PyPI) ECOSYSTEM:introduced=3.1.0,fixed=3.1.1.

**Is there a fix for CVE-2025-47278?** Yes. flask (PyPI): upgrade to 3.1.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2025-47278?** Check whether you run flask (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- flask (PyPI): upgrade to 3.1.1 or later

  ```sh
  pip install "flask>=3.1.1"
  ```


## Affected products

- flask (PyPI) ECOSYSTEM:introduced=3.1.0,fixed=3.1.1

## Identifiers

- CVE-2025-47278
- GHSA-4grg-w6v8-c28g
- PYSEC-2026-1377

## Related threats

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- [Flask vulnerable to possible disclosure of permanent session cookie due to missing Vary: Cookie header](https://junglewise.ai/threats/cve-2023-30861-flask-vulnerable-to-possible-disclosure-of-permanent-session)
- [Pallets Project Flask is vulnerable to Denial of Service via Unexpected memory usage](https://junglewise.ai/threats/cve-2019-1010083-pallets-project-flask-is-vulnerable-to-denial-of-service-via)
- [Flask is vulnerable to Denial of Service via incorrect encoding of JSON data](https://junglewise.ai/threats/cve-2018-1000656-flask-is-vulnerable-to-denial-of-service-via-incorrect-encoding)