CVE-2018-1000656: Flask Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-562c-5r94-xh97
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CVSS 7.5
CWE-20
Published
Advisory Summary

CVE-2018-1000656 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-20: Improper Input Validation) affecting Flask libraries in the PyPI ecosystem. The issue involves flask is vulnerable to denial of service via incorrect encoding of json data. Remediation is available by upgrading affected packages to version 0.12.3.

CVE-2018-1000656 at a Glance

CVE Identifier CVE-2018-1000656
GHSA Identifier GHSA-562c-5r94-xh97
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-20: Improper Input Validation
Affected Product Flask
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2018-1000656

To remediate this vulnerability, upgrade all affected Flask dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Flask fixed: 0.12.3 
pip install Flask>=0.12.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show Flask

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2018-1000656, inspect your installed packages using pip:

pip show Flask

Analyze the terminal output to locate any version of Flask in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.12.3), your application is affected.

Note: The pip show Flask command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In Flask, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2018-1000656 Affected Flask Versions

1 component(s)
Fixed Versions:
0.12.3
Product / Package Ecosystem Affected Versions Fixed Version
Flask
pypi/Flask
PyPI
< 0.12.3
0.12.3

References

NVD — CVE-2018-1000656 NVD
https://nvd.nist.gov/vuln/detail/CVE-2018-1000656
Flask Source Repository REPOSITORY
https://github.com/pallets/flask/pull/2691
Security Fix Commit FIX COMMIT
https://github.com/pallets/flask/commit/b178e89e4456e777b1a7ac6d7199052d0dfdbbbe
GitHub Advisory / Wiki ADVISORY
https://github.com/advisories/GHSA-562c-5r94-xh97
Flask Source Repository REPOSITORY
https://github.com/pallets/flask
Flask Release RELEASE
https://github.com/pallets/flask/releases/tag/0.12.3
Flask Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/flask/PYSEC-2018-66.yaml
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2019/08/msg00025.html
Flask Security Information SECURITY
https://security.netapp.com/advisory/ntap-20190221-0001
usn.ubuntu.com/4378-1 WEB
https://usn.ubuntu.com/4378-1

Frequently Asked Questions

What is CVE-2018-1000656?
CVE-2018-1000656 is a security vulnerability in Flask involving Flask is vulnerable to Denial of Service via incorrect encoding of JSON data under CWE-20: Improper Input Validation.
Which Flask versions are affected?
Affected versions include releases prior to 0.12.3 across affected packages: Flask.
What version fixes CVE-2018-1000656?
Upgrading to 0.12.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is Flask affected?
Yes, Flask is affected in releases prior to 0.12.3. Upgrade your dependency to 0.12.3 or later.
What is the CVSS score of CVE-2018-1000656?
CVE-2018-1000656 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2018-1000656?
CVE-2018-1000656 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check PyPI dependencies for CVE-2018-1000656?
Run the dependency tree command: 'pip show Flask'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-562c-5r94-xh97",
  "modified" : "2024-09-20T20:16:29Z",
  "published" : "2018-08-23T19:10:40Z",
  "aliases" : [ "CVE-2018-1000656" ],
  "summary" : "Flask is vulnerable to Denial of Service via incorrect encoding of JSON data",
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "Flask"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.12.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2018-1000656"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pallets/flask/pull/2691"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pallets/flask/commit/b178e89e4456e777b1a7ac6d7199052d0dfdbbbe"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-562c-5r94-xh97"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/pallets/flask"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pallets/flask/releases/tag/0.12.3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/flask/PYSEC-2018-66.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2019/08/msg00025.html"
  }, {
    "type" : "WEB",
    "url" : "https://security.netapp.com/advisory/ntap-20190221-0001"
  }, {
    "type" : "WEB",
    "url" : "https://usn.ubuntu.com/4378-1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-06-16T21:00:05Z",
    "nvd_published_at" : null
  }
}