CVE-2021-29433: Matrix sydent Remote Code Execution Vulnerability

MODERATE
Advisory Identifier: GHSA-pw4v-gr34-2553
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CVSS 4.3
CWE-400 CWE-20
Published
Advisory Summary

CVE-2021-29433 is a MODERATE (CVSS 4.3) remote code execution vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Matrix sydent libraries in the PyPI ecosystem. The issue involves sydent dos (via resource exhaustion) due to improper input validation. Remediation is available by upgrading affected packages to version 2.3.0.

CVE-2021-29433 at a Glance

CVE Identifier CVE-2021-29433
GHSA Identifier GHSA-pw4v-gr34-2553
Severity MODERATE
CVSS v3.1 Base Score 4.3
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Matrix sydent
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 4.3

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

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

How to Fix CVE-2021-29433

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

matrix-sydent fixed: 2.3.0 
pip install matrix-sydent>=2.3.0
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 matrix-sydent

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-29433, inspect your installed packages using pip:

pip show matrix-sydent

Analyze the terminal output to locate any version of Matrix sydent in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.3.0), your application is affected.

Note: The pip show matrix-sydent 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 Matrix sydent, 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 Missing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. ### Patches Fixed by 3175fd3. ### For more information If you have any questions or comments about this advisory, email us at security@matrix.org.

CVE-2021-29433 Affected Matrix sydent Versions

1 component(s)
Fixed Versions:
2.3.0
Product / Package Ecosystem Affected Versions Fixed Version
matrix-sydent
pypi/matrix-sydent
PyPI
< 2.3.0
2.3.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/matrix-org/sydent/security/advisories/GHSA-pw4v-gr34-2553
NVD — CVE-2021-29433 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-29433
Security Fix Commit FIX COMMIT
https://github.com/matrix-org/sydent/commit/3175fd358ebc2c310eab7a3dbf296ce2bd54c1da
Matrix sydent Source Repository REPOSITORY
https://github.com/matrix-org/sydent
Matrix sydent Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-24.yaml
pypi.org/project/matrix-syde... WEB
https://pypi.org/project/matrix-sydent

Frequently Asked Questions

What is CVE-2021-29433?
CVE-2021-29433 is a security vulnerability in Matrix sydent involving Sydent DoS (via resource exhaustion) due to improper input validation under CWE-400: Uncontrolled Resource Consumption.
Which Matrix sydent versions are affected?
Affected versions include releases prior to 2.3.0 across affected packages: matrix-sydent.
What version fixes CVE-2021-29433?
Upgrading to 2.3.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is matrix-sydent affected?
Yes, matrix-sydent is affected in releases prior to 2.3.0. Upgrade your dependency to 2.3.0 or later.
What is the CVSS score of CVE-2021-29433?
CVE-2021-29433 has a CVSS v3.1 base score of 4.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2021-29433?
CVE-2021-29433 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-2021-29433?
Run the dependency tree command: 'pip show matrix-sydent'. 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-pw4v-gr34-2553",
  "modified" : "2024-09-24T15:42:42Z",
  "published" : "2021-04-16T19:53:37Z",
  "aliases" : [ "CVE-2021-29433" ],
  "summary" : "Sydent DoS (via resource exhaustion) due to improper input validation",
  "details" : "### Impact\n\nMissing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion.\n\n### Patches\n\nFixed by 3175fd3.\n\n### For more information\n\nIf you have any questions or comments about this advisory, email us at security@matrix.org.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "matrix-sydent"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.3.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/sydent/security/advisories/GHSA-pw4v-gr34-2553"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-29433"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/sydent/commit/3175fd358ebc2c310eab7a3dbf296ce2bd54c1da"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/matrix-org/sydent"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-24.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/matrix-sydent"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-400" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-04-15T18:45:07Z",
    "nvd_published_at" : "2021-04-15T18:15:00Z"
  }
}