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Fencer Vulns
critical 9.8

CVE-2021-3520 json

There's a flaw in lz4.

published 2021-06-02 5 y ago modified 2026-10-14 26 d ago also EUVD-2021-26836 , JLSEC-2026-532

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.4%
EPSS 3.4% chance of exploitation in 30 days, percentile 88%
public exploits
0
none known

Summary

There's a flaw in lz4. An attacker who submits a crafted file to an application linked with lz4 may be able to trigger an integer overflow, leading to calling of memmove() on a negative size argument, causing an out-of-bounds write and/or a crash. The greatest impact of this flaw is to availability, with some potential impact to confidentiality and integrity as well.

Patch / fix

  • julia Lz4_jll 1.9.4+0
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • lz4 Debian 14, Debian 13, Debian 12 1.9.3-2

debian advisories DEBIAN-CVE-2021-3520

  • lz4 Ubuntu 18.04 LTS 0.0~r131-2ubuntu3.1
  • lz4 Ubuntu 20.04 LTS 1.9.2-2ubuntu0.20.04.1
  • lz4 Ubuntu Pro 14.04 LTS 0.0~r114-2ubuntu1+esm2
  • lz4 Ubuntu Pro 16.04 LTS 0.0~r131-2ubuntu2+esm1

ubuntu advisories UBUNTU-CVE-2021-3520

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • lz4 RHEL 8 1.8.3-3.el8_4
  • lz4-libs RHEL 8 1.8.3-3.el8_4

red hat advisories RHSA-2021:2575

  • lz4 SLE Module for Basesystem 15 SP3 1.9.2-3.3.1
  • lz4 SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +12 more 1.8.0-3.8.1
  • lz4 SLE Software Development Kit 12 SP5 1.8.0-3.3.1

suse advisories SUSE-SU-2021:1825-1SUSE-SU-2021:1647-1SUSE-SU-2021:1613-1

  • lz4 openSUSE Tumbleweed 1.9.3-2.1
  • lz4 openSUSE Leap 15.3 1.9.2-3.3.1
  • lz4 openSUSE Leap 15.2 1.8.0-lp152.5.3.1
  • lz4-test openSUSE Leap 15.2 1.8.0-lp152.5.3.1

opensuse advisories openSUSE-SU-2024:11562-1openSUSE-SU-2021:1825-1openSUSE-SU-2021:0760-1

  • lz4 AlmaLinux 8 1.8.3-3.el8_4
  • lz4-libs AlmaLinux 8 1.8.3-3.el8_4

almalinux advisories ALSA-2021:2575

  • lz4 Rocky Linux 8 1.8.3-3.el8_4

rocky linux advisories RLSA-2021:2575

  • lz4 Alpine 3.13, Alpine 3.12 1.9.2-r1
  • lz4 Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 1.9.3-r1

alpine advisories ALPINE-CVE-2021-3520

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

  • lz4 Arch Linux 1:1.9.3-2

arch linux advisories AVG-1889

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-2021-3520 updated cvss 8.6

lz4: memory corruption due to an integer overflow bug caused by memmove argument

  • Red Hat build of Quarkus lz4
    affected: no fix available
  • Red Hat Enterprise Linux 7 lz4
    affected: no fix planned “Out of support scope”
  • Red Hat Fuse 7 lz4
    affected: no fix available “Fix deferred”
  • Red Hat Integration Camel Quarkus 1 lz4
    affected: no fix available
  • Red Hat JBoss Fuse 6 lz4
    affected: no fix planned “Out of support scope”
  • Red Hat AMQ Streams 2.1.0
    fixed: vendor fix RHSA-2022:1345
  • Red Hat AMQ Streams 2.7.0
    fixed: vendor fix RHSA-2024:3527
  • Red Hat Enterprise Linux BaseOS (v. 8) lz4 1.8.3-3.el8_4, lz4-libs 1.8.3-3.el8_4
    fixed: vendor fix RHSA-2021:2575
show 4 more
  • Red Hat Migration Toolkit 1.4 rhmtc/openshift-migration-ui-rhel8 v1.4.6-4, rhmtc/openshift-velero-plugin-rhel8 v1.4.6-4, rhmtc/openshift-migration-velero-rhel8 v1.4.6-5, rhmtc/openshift-migration-registry-rhel8 v1.4.6-4, rhmtc/openshift-migration-operator-bundle v1.4.6-5, rhmtc/openshift-migration-controller-rhel8 v1.4.6-4, +7 more
    fixed: vendor fix RHBA-2021:2854
  • Red Hat RHAF Camel-K 1.8
    fixed: vendor fix RHSA-2022:6407
  • Red Hat RHINT Camel-Q 2.7
    fixed: vendor fix RHSA-2022:5606
  • Red Hat Advanced Cluster Management for Kubernetes 2 lz4 Red Hat Enterprise Linux 9 lz4, lz4-libs
    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

cisa ICSA-23-348-10 updated cvss 9.8

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
31 d ago

Exploit prediction

3.40% chance of exploitation in the next 30 days, higher than 88% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
OSV 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
julia Lz4_jll
<1.9.4+0
1.9.4+0

Affected products

  • n/a lz4
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

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.