CVE-2021-21273: Matrix synapse Open Redirects On Some Federation Vulnerability
MODERATECVE-2021-21273 is a MODERATE (CVSS 3.1) open redirects on some federation vulnerability (CWE-601: URL Redirection to Untrusted Site ('Open Redirect')) affecting Matrix synapse libraries in the PyPI ecosystem. The issue involves open redirects on some federation and push requests. Remediation is available by upgrading affected packages to version 1.25.0.
CVE-2021-21273 at a Glance
Security Impact
CVSS: 3.1
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N).
How to Fix CVE-2021-21273
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.
pip install matrix-synapse>=1.25.0Run the following command in your project directory to verify that all resolved dependencies use the patched release:
pip show matrix-synapseHow to Check if You Are Affected
To determine whether your Python environment is affected by CVE-2021-21273, inspect your installed packages using pip:
pip show matrix-synapseAnalyze 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 1.25.0), 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-601: URL Redirection to Untrusted Site ('Open Redirect'), where the web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect. 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
CVE-2021-21273 Affected Matrix synapse Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
matrix-synapse
|
PyPI |
< 1.25.0
|
1.25.0
|
References
Frequently Asked Questions
What is CVE-2021-21273?
Which Matrix synapse versions are affected?
What version fixes CVE-2021-21273?
Is matrix-synapse affected?
What is the CVSS score of CVE-2021-21273?
What CWE is associated with CVE-2021-21273?
How can I check PyPI dependencies for CVE-2021-21273?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-v936-j8gp-9q3p",
"modified" : "2024-09-24T15:35:29Z",
"published" : "2021-02-26T17:28:34Z",
"aliases" : [ "CVE-2021-21273" ],
"summary" : "Open redirects on some federation and push requests",
"details" : "### Impact\nRequests to user provided domains were not restricted to external IP addresses when calculating the key validity for third-party invite events and sending push notifications. This could cause Synapse to make requests to internal infrastructure. The type of request was not controlled by the user, although limited modification of request bodies was possible.\n\nFor the most thorough protection server administrators should remove the deprecated `federation_ip_range_blacklist` from their settings after upgrading to Synapse v1.25.0 which will result in Synapse using the improved default IP address restrictions. See the new `ip_range_blacklist` and `ip_range_whitelist` settings if more specific control is necessary.\n\n### Patches\nIssue is resolved by #8821. Further improvements to protect homeservers by default were made in #8870 and #8954.\n\n### Workarounds\nRequests to internal IP addresses could be blocked at the system or network level.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N"
}, {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "PyPI",
"name" : "matrix-synapse"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "1.25.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/matrix-org/synapse/security/advisories/GHSA-v936-j8gp-9q3p"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-21273"
}, {
"type" : "WEB",
"url" : "https://github.com/matrix-org/synapse/pull/8821"
}, {
"type" : "WEB",
"url" : "https://github.com/matrix-org/synapse/commit/30fba6210834a4ecd91badf0c8f3eb278b72e746"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/matrix-org/synapse"
}, {
"type" : "WEB",
"url" : "https://github.com/matrix-org/synapse/releases/tag/v1.25.0"
}, {
"type" : "WEB",
"url" : "https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-131.yaml"
}, {
"type" : "WEB",
"url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-601" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2021-02-26T17:26:48Z",
"nvd_published_at" : "2021-02-26T18:15:00Z"
}
}