CVE-2021-3405

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of service disruption.

Exploit odds

1.7% chance of exploitation in the next 30 days (EPSS).

Fix

No patch or advisory is linked yet. Look at mitigations or restrict exposure.

Timeline

1. 2021-02-23 20:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 04:05 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.7% in the next 30 days (EPSS).
• Severity: 6.5 MEDIUM (CVSS).
• Fix: none linked yet, which raises it.

Details

Published

2021-02-23 20:15 UTC

Last modified

2026-06-17 04:05 UTC

Exploit probability

1.7% · EPSS, next 30 days

Weakness

CWE-787 · Out-of-bounds write

Record status

Modified

Affected

• Matroska Libebml < 1.4.2
• Fedoraproject Fedora 32
• Fedoraproject Fedora 33
• Fedoraproject Fedora 34
• Debian Linux 9.0

Attack profile CVSS 3.1 · 6.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-3405.md and follow it. Check whether this project is affected by CVE-2021-3405. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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