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Fencer Vulns
medium 6.5

CVE-2021-3405 json

A flaw was found in libebml before 1.4.2.

published 2021-02-23 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26733

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 77%
public exploits
0
none known

Summary

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.

Patch / fix

  • matroska libebml 1.4.2
  • libebml Debian 14, Debian 13, Debian 12 1.4.2-1

debian advisories DEBIAN-CVE-2021-3405

  • libebml Alpine 3.24, Alpine 3.23, Alpine 3.22 +9 more 1.4.2-r0

alpine advisories ALPINE-CVE-2021-3405

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libebml Arch Linux 1.4.2-1

arch linux advisories AVG-1554

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3405 updated cvss 7.5

libebml: Heap overflow in EbmlString::ReadData and EbmlUnicodeString::ReadData

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.73% chance of exploitation in the next 30 days, higher than 77% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/Matroska-Org/libebml/issues/74 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:N/A:P

Affected products

  • n/a libebml

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.