CVE-2020-26890: Matrix synapse Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-4mp3-385r-v63f
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CVSS 7.5
CWE-20
Published
Advisory Summary

CVE-2020-26890 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-20: Improper Input Validation) affecting Matrix synapse libraries in the PyPI ecosystem. The issue involves denial of service attack due to invalid json. Remediation is available by upgrading affected packages to version 1.20.0.

CVE-2020-26890 at a Glance

CVE Identifier CVE-2020-26890
GHSA Identifier GHSA-4mp3-385r-v63f
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-20: Improper Input Validation
Affected Product Matrix synapse
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-2020-26890

To remediate this vulnerability, upgrade all affected Matrix synapse 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-synapse fixed: 1.20.0 
pip install matrix-synapse>=1.20.0
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-synapse

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2020-26890, inspect your installed packages using pip:

pip show matrix-synapse

Analyze the terminal output to locate any version of Matrix synapse in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.20.0), your application is affected.

Note: The pip show matrix-synapse 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 Matrix synapse, 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 denial of service attack against Matrix clients can be exploited by sending an event including invalid JSON data to Synapse. Synapse would relay the data to clients which could crash or hang. Impact is long-lasting if the event is made part of the room state. ### Patches At a minimum #8106 and #8291 must be applied. #7372 and #8124 include additional checks. ### Workarounds There are no known workarounds. ### Upgrading notes If an invalid event is accepted by an earlier Synapse it can become part of the room state and will not be fixed by upgrading Synapse. Redacting the invalid event should avoid clients receiving the invalid event.

CVE-2020-26890 Affected Matrix synapse Versions

1 component(s)
Fixed Versions:
1.20.0
Product / Package Ecosystem Affected Versions Fixed Version
matrix-synapse
pypi/matrix-synapse
PyPI
< 1.20.0
1.20.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/matrix-org/synapse/security/advisories/GHSA-4mp3-385r-v63f
NVD — CVE-2020-26890 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-26890
Matrix synapse Source Repository REPOSITORY
https://github.com/matrix-org/synapse
Matrix synapse Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2020-237.yaml
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/G7YXMMYQP46PYL664JQUXCA3LPBJU7DQ
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/U34DPP4ZLOEDUY2ZCWOHQPU5GA5LYNUQ
pypi.org/project/matrix-syna... WEB
https://pypi.org/project/matrix-synapse

Frequently Asked Questions

What is CVE-2020-26890?
CVE-2020-26890 is a security vulnerability in Matrix synapse involving Denial of service attack due to invalid JSON under CWE-20: Improper Input Validation.
Which Matrix synapse versions are affected?
Affected versions include releases prior to 1.20.0 across affected packages: matrix-synapse.
What version fixes CVE-2020-26890?
Upgrading to 1.20.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is matrix-synapse affected?
Yes, matrix-synapse is affected in releases prior to 1.20.0. Upgrade your dependency to 1.20.0 or later.
What is the CVSS score of CVE-2020-26890?
CVE-2020-26890 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-2020-26890?
CVE-2020-26890 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-2020-26890?
Run the dependency tree command: 'pip show matrix-synapse'. 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-4mp3-385r-v63f",
  "modified" : "2024-09-30T20:31:47Z",
  "published" : "2020-11-24T22:58:58Z",
  "aliases" : [ "CVE-2020-26890" ],
  "summary" : "Denial of service attack due to invalid JSON",
  "details" : "### Impact\nA denial of service attack against Matrix clients can be exploited by sending an event including invalid JSON data to Synapse. Synapse would relay the data to clients which could crash or hang. Impact is long-lasting if the event is made part of the room state.\n\n### Patches\nAt a minimum #8106 and #8291 must be applied. #7372 and #8124 include additional checks.\n\n### Workarounds\nThere are no known workarounds.\n\n### Upgrading notes\nIf an invalid event is accepted by an earlier Synapse it can become part of the room state and will not be fixed by upgrading Synapse. Redacting the invalid event should avoid clients receiving the invalid event.",
  "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-synapse"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.20.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/matrix-org/synapse/security/advisories/GHSA-4mp3-385r-v63f"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-26890"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/matrix-org/synapse"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2020-237.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/G7YXMMYQP46PYL664JQUXCA3LPBJU7DQ"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/U34DPP4ZLOEDUY2ZCWOHQPU5GA5LYNUQ"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/matrix-synapse"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-11-24T21:47:35Z",
    "nvd_published_at" : "2020-11-24T03:15:00Z"
  }
}