CVE-2021-29430: Matrix sydent Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-wmg4-8cp2-hpg9
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CVSS 7.5
CWE-400 CWE-20 CWE-770
Published
Advisory Summary

CVE-2021-29430 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Matrix sydent libraries in the PyPI ecosystem. The issue involves sydent vulnerable to denial of service attack via memory exhaustion. Remediation is available by upgrading affected packages to version 2.3.0.

CVE-2021-29430 at a Glance

CVE Identifier CVE-2021-29430
GHSA Identifier GHSA-wmg4-8cp2-hpg9
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Matrix sydent
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-2021-29430

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-2021-29430, 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 Sydent does not limit the size of requests it receives from HTTP clients. A malicious user could send an HTTP request with a very large body, leading to disk space exhaustion and denial of service. Sydent also does not limit response size for requests it makes to remote Matrix homeservers. A malicious homeserver could return a very large response, again leading to memory exhaustion and denial of service. This affects any server which accepts registration requests from untrusted clients. ### Patches Patched by 89071a1, 0523511, f56eee3. ### Workarounds Request sizes can be limited in an HTTP reverse-proxy. There are no known workarounds for the problem with overlarge responses. ### For more information If you have any questions or comments about this advisory, email us at security@matrix.org.

CVE-2021-29430 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-wmg4-8cp2-hpg9
NVD — CVE-2021-29430 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-29430
Security Fix Commit FIX COMMIT
https://github.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7
Security Fix Commit FIX COMMIT
https://github.com/matrix-org/sydent/commit/89071a1a754c69a50deac89e6bb74002d4cda19d
Security Fix Commit FIX COMMIT
https://github.com/matrix-org/sydent/commit/f56eee315b6c44fdd9f6aa785cc2ec744a594428
Matrix sydent Source Repository REPOSITORY
https://github.com/matrix-org/sydent
Matrix sydent Release RELEASE
https://github.com/matrix-org/sydent/releases/tag/v2.3.0
Matrix sydent Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-21.yaml
pypi.org/project/matrix-syde... WEB
https://pypi.org/project/matrix-sydent

Frequently Asked Questions

What is CVE-2021-29430?
CVE-2021-29430 is a security vulnerability in Matrix sydent involving Sydent vulnerable to denial of service attack via memory exhaustion 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-2021-29430?
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-2021-29430?
CVE-2021-29430 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-2021-29430?
CVE-2021-29430 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-2021-29430?
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-wmg4-8cp2-hpg9",
  "modified" : "2024-09-24T15:43:44Z",
  "published" : "2021-04-19T14:54:04Z",
  "aliases" : [ "CVE-2021-29430" ],
  "summary" : "Sydent vulnerable to denial of service attack via memory exhaustion",
  "details" : "### Impact\n\nSydent does not limit the size of requests it receives from HTTP clients. A malicious user could send an HTTP request with a very large body, leading to disk space exhaustion and denial of service.\n\nSydent also does not limit response size for requests it makes to remote Matrix homeservers. A malicious homeserver could return a very large response, again leading to memory exhaustion and denial of service.\n\nThis affects any server which accepts registration requests from untrusted clients.\n\n### Patches\n\nPatched by 89071a1, 0523511, f56eee3.\n\n### Workarounds\n\nRequest sizes can be limited in an HTTP reverse-proxy.\n\nThere are no known workarounds for the problem with overlarge responses.\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: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" : "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-wmg4-8cp2-hpg9"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-29430"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/sydent/commit/89071a1a754c69a50deac89e6bb74002d4cda19d"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/sydent/commit/f56eee315b6c44fdd9f6aa785cc2ec744a594428"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/matrix-org/sydent"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/sydent/releases/tag/v2.3.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-21.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/matrix-sydent"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-400", "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-04-15T20:49:34Z",
    "nvd_published_at" : "2021-04-15T21:15:00Z"
  }
}