CVE-2024-3651: Idna Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-jjg7-2v4v-x38h
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CVSS 6.2
CWE-400 CWE-1333
Published
Advisory Summary

CVE-2024-3651 is a MODERATE (CVSS 6.2) denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Idna libraries in the PyPI ecosystem. The issue involves internationalized domain names in applications (idna) vulnerable to denial of service from specially crafted inputs to idna.encode. Remediation is available by upgrading affected packages to version 3.7.

CVE-2024-3651 at a Glance

CVE Identifier CVE-2024-3651
GHSA Identifier GHSA-jjg7-2v4v-x38h
Severity MODERATE
CVSS v3.1 Base Score 6.2
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Idna
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 6.2

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

Attack Vector Local (AV:L)
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-2024-3651

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

idna fixed: 3.7 
pip install idna>=3.7
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 idna

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2024-3651, inspect your installed packages using pip:

pip show idna

Analyze the terminal output to locate any version of Idna in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.7), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Idna, 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

### Impact A specially crafted argument to the `idna.encode()` function could consume significant resources. This may lead to a denial-of-service. ### Patches The function has been refined to reject such strings without the associated resource consumption in version 3.7. ### Workarounds Domain names cannot exceed 253 characters in length, if this length limit is enforced prior to passing the domain to the `idna.encode()` function it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application. ### References * https://huntr.com/bounties/93d78d07-d791-4b39-a845-cbfabc44aadb

CVE-2024-3651 Affected Idna Versions

1 component(s)
Fixed Versions:
3.7
Product / Package Ecosystem Affected Versions Fixed Version
idna
pypi/idna
PyPI
< 3.7
3.7

References

GitHub Advisory / Wiki ADVISORY
https://github.com/kjd/idna/security/advisories/GHSA-jjg7-2v4v-x38h
NVD — CVE-2024-3651 NVD
https://nvd.nist.gov/vuln/detail/CVE-2024-3651
Security Fix Commit FIX COMMIT
https://github.com/kjd/idna/commit/1d365e17e10d72d0b7876316fc7b9ca0eebdd38d
Idna Source Repository REPOSITORY
https://github.com/kjd/idna
Idna Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/idna/PYSEC-2024-60.yaml
huntr.com/bounties/93d78d07-d... WEB
https://huntr.com/bounties/93d78d07-d791-4b39-a845-cbfabc44aadb
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2024/05/msg00006.html
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4YQUPYH3SVZ5GFF2CDQ55FCM575AZTF2
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/F2S5E23N6E52S46KGNYTDFB75LOC4N4D
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/S5IDLLD2IKSIVRBSLB34WTSYGLMWUFWF
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ULSC7HBJKXB3BZV367WM5BR6DFEC4Z43

Frequently Asked Questions

What is CVE-2024-3651?
CVE-2024-3651 is a security vulnerability in Idna involving Internationalized Domain Names in Applications (IDNA) vulnerable to denial of service from specially crafted inputs to idna.encode under CWE-400: Uncontrolled Resource Consumption.
Which Idna versions are affected?
Affected versions include releases prior to 3.7 across affected packages: idna.
What version fixes CVE-2024-3651?
Upgrading to 3.7 (or the latest patched release for your respective branch) resolves the vulnerability.
Is idna affected?
Yes, idna is affected in releases prior to 3.7. Upgrade your dependency to 3.7 or later.
What is the CVSS score of CVE-2024-3651?
CVE-2024-3651 has a CVSS v3.1 base score of 6.2 (MODERATE) with vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2024-3651?
CVE-2024-3651 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check PyPI dependencies for CVE-2024-3651?
Run the dependency tree command: 'pip show idna'. 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-jjg7-2v4v-x38h",
  "modified" : "2025-11-05T20:10:47Z",
  "published" : "2024-04-11T21:32:40Z",
  "aliases" : [ "CVE-2024-3651" ],
  "summary" : "Internationalized Domain Names in Applications (IDNA) vulnerable to denial of service from specially crafted inputs to idna.encode",
  "details" : "### Impact\nA specially crafted argument to the `idna.encode()` function could consume significant resources. This may lead to a denial-of-service.\n\n### Patches\nThe function has been refined to reject such strings without the associated resource consumption in version 3.7.\n\n### Workarounds\nDomain names cannot exceed 253 characters in length, if this length limit is enforced prior to passing the domain to the `idna.encode()` function it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application.\n\n### References\n* https://huntr.com/bounties/93d78d07-d791-4b39-a845-cbfabc44aadb",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/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" : "idna"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.7"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/kjd/idna/security/advisories/GHSA-jjg7-2v4v-x38h"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2024-3651"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/kjd/idna/commit/1d365e17e10d72d0b7876316fc7b9ca0eebdd38d"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/kjd/idna"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/idna/PYSEC-2024-60.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://huntr.com/bounties/93d78d07-d791-4b39-a845-cbfabc44aadb"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2024/05/msg00006.html"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4YQUPYH3SVZ5GFF2CDQ55FCM575AZTF2"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/F2S5E23N6E52S46KGNYTDFB75LOC4N4D"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/S5IDLLD2IKSIVRBSLB34WTSYGLMWUFWF"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ULSC7HBJKXB3BZV367WM5BR6DFEC4Z43"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333", "CWE-400" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2024-04-11T21:32:40Z",
    "nvd_published_at" : "2024-07-07T18:15:09Z"
  }
}