Medium severity6.1NVD Advisory· Published Mar 26, 2021· Updated Jun 17, 2026
CVE-2021-21333
CVE-2021-21333
Description
Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the notification emails sent for notifications for missed messages or for an expiring account are subject to HTML injection. In the case of the notification for missed messages, this could allow an attacker to insert forged content into the email. The account expiry feature is not enabled by default and the HTML injection is not controllable by an attacker. This is fixed in version 1.27.0.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
matrix-synapsePyPI | < 1.27.0 | 1.27.0 |
Affected products
4cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*+ 1 more
- cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*range: <1.27.0
- (no CPE)range: < 1.27.0
- cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
Patches
Vulnerability mechanics
References
9- github.com/matrix-org/synapse/commit/e54746bdf7d5c831eabe4dcea76a7626f1de73dfnvdPatchThird Party AdvisoryWEB
- github.com/matrix-org/synapse/pull/9200nvdPatchThird Party AdvisoryWEB
- github.com/matrix-org/synapse/security/advisories/GHSA-c5f8-35qr-q4fmnvdPatchThird Party AdvisoryWEB
- github.com/advisories/GHSA-c5f8-35qr-q4fmghsaADVISORY
- github.com/matrix-org/synapse/releases/tag/v1.27.0nvdThird Party AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2021-21333ghsaADVISORY
- github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-134.yamlghsaWEB
- lists.fedoraproject.org/archives/list/[email protected]/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEYghsaWEB
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/nvd
News mentions
0No linked articles in our index yet.