Flask is vulnerable to Denial of Service via incorrect encoding of JSON data
The Pallets Project flask version Before 0.12.3 contains a CWE-20: Improper Input Validation vulnerability in flask that can result in Large amount of memory usage possibly leading to denial of service. This attack appear to be exploitable via Attacker provides JSON data in incorrect encoding. This vulnerability appears to have been fixed in 0.12.3.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | flask | < 0.12.3 | 0.12.3 |
References
- https://github.com/pallets/flask/releases/tag/0.12.3
- https://github.com/pallets/flask/pull/2691
- https://security.netapp.com/advisory/ntap-20190221-0001/
- https://lists.debian.org/debian-lts-announce/2019/08/msg00025.html
- https://usn.ubuntu.com/4378-1/
- https://github.com/advisories/GHSA-562c-5r94-xh97
- https://nvd.nist.gov/vuln/detail/CVE-2018-1000656
- https://github.com/pallets/flask/commit/b178e89e4456e777b1a7ac6d7199052d0dfdbbbe
- https://github.com/pallets/flask
- https://github.com/pypa/advisory-database/tree/main/vulns/flask/PYSEC-2018-66.yaml
- https://security.netapp.com/advisory/ntap-20190221-0001
- https://usn.ubuntu.com/4378-1
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-20- Platform
- Python (PyPI)
- Package
flask- Disclosed
- 20.08.2018
- Updated
- 11.10.2026 12:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2018-66 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-562c-5r94-xh97 - CC BY 4.0
Vulnerability history: flask
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 08.2018 02.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 3
- Low 2
Disclosures per year
- 2018: 1
- 2019: 1
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 1
- 2024: 0
- 2025: 1
- 2026: 1
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Flask is vulnerable to Denial of Service via incorrect encoding of JSON data this entry
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