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Not in CISA KEV
MEDIUM severity

CVE-2021-29432 — matrix-sydent

MEDIUMFix: matrix-org/sydent@4469d1d

CVE-2021-29432 is a medium-severity (CVSS 5.7) Improper Input Validation vulnerability in matrix-sydent. A fix is available for matrix-sydent — see the affected versions and patch details below.

Malicious users could abuse Sydent to control the content of invitation emails

Also known asGHSA-mh74-4m5g-fcjxPYSEC-2021-23
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 1, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.9%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs61th percentile — riskier than 61% of all scored CVEsHighest risk
0.00%0.48%0.96%1.43%0.3%0.9%May 26Aug 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐍matrix-sydent

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

A malicious user could abuse Sydent to send out arbitrary emails from the Sydent email address. This could be used to construct plausible phishing emails, for example.

Patches

Fixed in 4469d1d, 6b405a8, 65a6e91.

Note that these patches include changes to the default email templates. If these templates have been locally modified, they must also be updated.

For more information

If you have any questions or comments about this advisory, email us at [email protected].

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPImatrix-sydentall versions2.3.0pip install --upgrade 'matrix-sydent==2.3.0'

Affected Products

1 product · 1 configurations
Application
sydentmatrix
< 2.3.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-sydent, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update matrix-sydent to 2.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29432 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact A malicious user could abuse Sydent to send out arbitrary emails from the Sydent email address. This could be used to construct plausible phishing emails, for example. ### Patches Fixed in 4469d1d, 6b405a8, 65a6e91. Note that these patches include changes to the *default* email templates. If these templates have been locally modified, they must also be updated. ### For more information If you have any questions or comments about this advisory, email us at [email protected].
O3 Security · Impact-Aware SCA

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CVE-2021-29432: matrix-sydent — Fixed in 2.3.0