How severe is CVE-2021-34813?

CVE-2021-34813 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-34813 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34813?

CVE-2021-34813 affects Matrix Olm. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-34813?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-34813 published?

CVE-2021-34813 was published on 2021-06-16 and last updated on 2026-06-17.

CVE-2021-34813

CVE-2021-34813 is a critical-severity vulnerability in Matrix Olm with a CVSS 3.x base score of 9.8. 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-787.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 4% (90th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Matrix Olm
Published: 2021-06-16
Last modified: 2026-06-17

Description

Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve an Olm encrypted room key backup from the homeserver) because olm_pk_decrypt has a stack-based buffer overflow. Remote code execution might be possible for some nonstandard build configurations.

Frequently asked questions

What is CVE-2021-34813?: Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve an Olm encrypted room key backup from the homeserver) because olm_pk_decrypt has a stack-based buffer overflow. Remote code execution might be possible for some nonstandard build configurations.
How severe is CVE-2021-34813?: CVE-2021-34813 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-34813 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 4% (90th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34813?: CVE-2021-34813 affects Matrix Olm. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-34813?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-34813 published?: CVE-2021-34813 was published on 2021-06-16 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:matrix:olm:*:*:*:*:*:*:*:*

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