CVE-2025-47278
Flask uses fallback key instead of current signing key
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
Attack profile
How easy it is to exploit
- Attack vector
- Local
- Complexity
- Low
- Privileges needed
- High
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
Exploit likelihood
What each source reports
CVE List Score used
Flask uses fallback key instead of current signing key
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
CVE-2025-47278- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-683
- Updated
- 2026-11-02
EUVDEUVD-2025-14386
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
EUVD-2025-14386- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-4grg-w6v8-c28g
Flask uses fallback key instead of current signing key
In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key.
Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first.
Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS are likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss.
- Record
GHSA-4grg-w6v8-c28g- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-683
- Updated
- 2026-11-02
NVD
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
CVE-2025-47278- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - Weakness
- CWE-683
- Updated
- 2026-11-02
OSV
Flask uses fallback key instead of current signing key
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
CVE-2025-47278- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-683
- Updated
- 2026-11-02
OSVDEBIAN-CVE-2025-47278
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
DEBIAN-CVE-2025-47278- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - Updated
- 2026-11-02
Show 7 moreShow less
OSVGHSA-4grg-w6v8-c28g
Flask uses fallback key instead of current signing key
In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key.
Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first.
Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS are likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss.
- Record
GHSA-4grg-w6v8-c28g- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-683
- Updated
- 2026-11-02
OSVPYSEC-2026-1377
Flask uses fallback key instead of current signing key
In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key.
Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first.
Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS are likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss.
- Record
PYSEC-2026-1377- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - Updated
- 2026-11-02
OSVUBUNTU-CVE-2025-47278
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
UBUNTU-CVE-2025-47278- CVSS 4.0
- 1.8 Low
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - Updated
- 2026-11-02
OSVAZL-77828 No score
CVE-2025-47278 affecting package python-flask 1.1.1-4
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
AZL-77828- Updated
- 2026-11-02
OSVAZL-77831 No score
CVE-2025-47278 affecting package python-flask 1.1.1-4
Flask is a web server gateway interface (WSGI) web application framework. In Flask 3.1.0, the way fallback key configuration was handled resulted in the last fallback key being used for signing, rather than the current signing key. Signing is provided by the itsdangerous library. A list of keys can be passed, and it expects the last (top) key in the list to be the most recent key, and uses that for signing. Flask was incorrectly constructing that list in reverse, passing the signing key first. Sites that have opted-in to use key rotation by setting SECRET_KEY_FALLBACKS care likely to unexpectedly be signing their sessions with stale keys, and their transition to fresher keys will be impeded. Sessions are still signed, so this would not cause any sort of data integrity loss. Version 3.1.1 contains a patch for the issue.
- Record
AZL-77831- Updated
- 2026-11-05
OSVopenSUSE-SU-2025:15152-1 No score
python311-Flask-3.1.1-1.1 on GA media
These are all security issues fixed in the python311-Flask-3.1.1-1.1 package on the GA media of openSUSE Tumbleweed.
- Record
openSUSE-SU-2025:15152-1- Updated
- 2026-11-02
OSVUSN-7534-1 No score
flask vulnerability
It was discovered that Flask incorrectly handled key rotation. An attacker could possibly use this issue to sign sessions with stale keys.
- Record
USN-7534-1- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
flaskPyPI |
3.1.0 to 3.1.0 | 3.1.1 |
python-flaskAzure Linux:2 |
through 1.1.1-4 | None known |
python-flaskAzure Linux:3 |
through 1.1.1-4 | None known |
flaskDebian:13 |
before 3.1.1-1 | 3.1.1-1 |
flaskDebian:14 |
before 3.1.1-1 | 3.1.1-1 |
flaskPyPI |
3.1.0 up to 3.1.1 | 3.1.1 |
flaskUbuntu:25.04 |
before 3.1.0-2ubuntu1.1, plus listed versions 3.0.3-1ubuntu13.1.0-2ubuntu1 |
3.1.0-2ubuntu1.1 |
python-FlaskopenSUSE:Tumbleweed |
before 3.1.1-1.1 | 3.1.1-1.1 |
History
| Recorded | Changed | Sources |
|---|---|---|
| facts | OSV | |
| affected | ||
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2025-47278 is a low vulnerability (CVSS 1.8) in Pallets Flask, published May 13, 2025. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.19%, the 8th percentile. Fixed in flask 3.1.1.
References
github.com/pallets/flask/security/advisories/GHSA-4grg-w6v8-c28g
nvd.nist.gov/vuln/detail/CVE-2025-47278
Show 8 moreShow less
security-tracker.debian.org/tracker/CVE-2025-47278
pypi.org/project/flask
ubuntu.com/security/CVE-2025-47278
cve.org/CVERecord?id=CVE-2025-47278
lists.opensuse.org/archives/list/[email protected]/thread/RQFGSNWSLQGT7NEERPR5OR67EM4FTVPJ
suse.com/security/cve/CVE-2025-47278