How severe is CVE-2021-29433?

CVE-2021-29433 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2021-29433 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-29433?

CVE-2021-29433 affects Matrix Sydent. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-29433?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-29433 published?

CVE-2021-29433 was published on 2021-04-15 and last updated on 2026-06-17.

CVE-2021-29433

CVE-2021-29433 is a medium-severity vulnerability in Matrix Sydent with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-400.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
CVSS v2: 4.0
EPSS exploit prediction: 1% (56th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-400
Affected product: Matrix Sydent
Published: 2021-04-15
Last modified: 2026-06-17

Description

Sydent is a reference Matrix identity server. In Sydent versions 2.2.0 and prior, sissing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. A patch for the vulnerability is in version 2.3.0. No workarounds are known to exist.

Frequently asked questions

What is CVE-2021-29433?: Sydent is a reference Matrix identity server. In Sydent versions 2.2.0 and prior, sissing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. A patch for the vulnerability is in version 2.3.0. No workarounds are known to exist.
How severe is CVE-2021-29433?: CVE-2021-29433 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2021-29433 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-29433?: CVE-2021-29433 affects Matrix Sydent. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-29433?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-29433 published?: CVE-2021-29433 was published on 2021-04-15 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:matrix:sydent:*:*:*:*:*:*:*:*

More vulnerabilities in Matrix Sydent

CVE-2023-38686 — Critical (CVSS 9.3): Sydent is an identity server for the Matrix communications protocol. Prior to version 2.5.6, if configured to send…
CVE-2021-29431 — High (CVSS 7.7): Sydent is a reference Matrix identity server. Sydent can be induced to send HTTP GET requests to internal systems, due…
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CVE-2019-11340 — Medium (CVSS 5.9): util/emailutils.py in Matrix Sydent before 1.0.2 mishandles registration restrictions that are based on e-mail domain,…
CVE-2021-29432 — Medium (CVSS 5.3): Sydent is a reference matrix identity server. A malicious user could abuse Sydent to send out arbitrary emails from the…

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