How severe is CVE-2021-3405?

CVE-2021-3405 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-3405 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3405?

CVE-2021-3405 primarily affects Matroska Libebml. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-3405?

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

When was CVE-2021-3405 published?

CVE-2021-3405 was published on 2021-02-23 and last updated on 2026-06-17.

CVE-2021-3405

CVE-2021-3405 is a medium-severity vulnerability in Matroska Libebml with a CVSS 3.x base score of 6.5. 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: Medium (CVSS 3.x base score 6.5)
CVSS v2: 4.3
EPSS exploit prediction: 2% (75th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Matroska Libebml
Published: 2021-02-23
Last modified: 2026-06-17

Description

A flaw was found in libebml before 1.4.2. A heap overflow bug exists in the implementation of EbmlString::ReadData and EbmlUnicodeString::ReadData in libebml.

Frequently asked questions

What is CVE-2021-3405?: A flaw was found in libebml before 1.4.2. A heap overflow bug exists in the implementation of EbmlString::ReadData and EbmlUnicodeString::ReadData in libebml.
How severe is CVE-2021-3405?: CVE-2021-3405 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-3405 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3405?: CVE-2021-3405 primarily affects Matroska Libebml. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-3405?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-3405 published?: CVE-2021-3405 was published on 2021-02-23 and last updated on 2026-06-17.

References

Affected products (5)

cpe:2.3:a:matroska:libebml:*:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

More vulnerabilities in Matroska Libebml

CVE-2015-8789 — Critical (CVSS 9.6): Use-after-free vulnerability in the EbmlMaster::Read function in libEBML before 1.3.3 allows context-dependent…
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CVE-2015-8791 — Medium (CVSS 4.3): The EbmlElement::ReadCodedSizeValue function in libEBML before 1.3.3 allows context-dependent attackers to obtain…
CVE-2015-8790 — Medium (CVSS 4.3): The EbmlUnicodeString::UpdateFromUTF8 function in libEBML before 1.3.3 allows context-dependent attackers to obtain…

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