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Fencer Vulns
medium 5.5

CVE-2021-24031 json

In the Zstandard command-line utility prior to v1.4.1, output files were created with default permissions.

published 2021-03-04 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-10951

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

In the Zstandard command-line utility prior to v1.4.1, output files were created with default permissions. Correct file permissions (matching the input) would only be set at completion time. Output files could therefore be readable or writable to unintended parties.

Patch / fix

  • Facebook Zstandard 1.4.1
  • libzstd Debian 14, Debian 13, Debian 12 1.4.8+dfsg-1

debian advisories DEBIAN-CVE-2021-24031

  • libzstd Ubuntu 18.04 LTS 1.3.3+dfsg-2ubuntu1.2
  • libzstd Ubuntu 20.04 LTS 1.4.4+dfsg-3ubuntu0.1
  • libzstd Ubuntu Pro 16.04 LTS 1.3.1+dfsg-1~ubuntu0.16.04.1+esm3

ubuntu advisories UBUNTU-CVE-2021-24031

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

  • zstd SLE Module for Basesystem 15 SP2, SLE Micro 5.0 1.4.4-1.6.1

suse advisories SUSE-SU-2021:0948-1

  • zstd openSUSE Leap 15.2 1.4.4-lp152.2.3.1

opensuse advisories openSUSE-SU-2021:0481-1

  • zstd Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 1.4.1-r0

alpine advisories ALPINE-CVE-2021-24031

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

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-2021-24031 updated cvss 5.5

zstd: adds read permissions to files while being compressed or uncompressed

  • Red Hat Ceph Storage 3 ceph, librbd1, librgw2, ceph-mds, ceph-mgr, ceph-mon, +15 more
    affected: no fix available “Fix deferred”
  • Red Hat OpenShift Container Platform 4 zstd, libzstd
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 zstd, libzstd Red Hat Enterprise Linux 9 zstd, libzstd Red Hat OpenStack Platform 16.1 zstd
    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

0.46% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/facebook/zstd/issues/1630 referenced PoC, tagged "exploit" by a source, unverified
  • bugs.debian.org https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=981404 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:P/I:N/A:N

Affected products

  • Facebook Zstandard

Classification

Weakness
  • CWE-277 Insecure Inherited Permissions
  • CWE-276 Incorrect Default Permissions

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.