What’s Vulnerable › Vulnerabilities

CVE-2021-3405

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.7% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-02-23 · updated 2026-06-17
• Weakness: CWE-787

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.

Affected products

• Debian Linux: 9.0
• Fedoraproject Fedora: 32, 33, 34
• Matroska Libebml: before 1.4.2 — fixed in 1.4.2

How to fix

Upgrade to a fixed version: Matroska Libebml 1.4.2. Check the vendor advisory for mitigations.

References

• https://github.com/Matroska-Org/libebml/issues/74
• https://lists.debian.org/debian-lts-announce/2021/04/msg00016.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JNHQI6MDOECJ2HT5GCLEX2DMJFEOWPW7/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UHIIMWZKHHELFF4NRDMOOCS3HKK3K4DF/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YY7R2JZRO5I6WS62KTJFTZGKYELVFTVB/
• https://security.gentoo.org/glsa/202208-21
• https://github.com/Matroska-Org/libebml/issues/74
• https://lists.debian.org/debian-lts-announce/2021/04/msg00016.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JNHQI6MDOECJ2HT5GCLEX2DMJFEOWPW7/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UHIIMWZKHHELFF4NRDMOOCS3HKK3K4DF/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YY7R2JZRO5I6WS62KTJFTZGKYELVFTVB/
• https://security.gentoo.org/glsa/202208-21

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