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Fencer Vulns
critical 9.8

CVE-2021-33574 json

The mq_notify function in the GNU C Library (aka glibc) versions 2.32 and 2.33 has a use-after-free.

published 2021-05-25 5 y ago modified 2026-10-14 26 d ago also EUVD-2021-20261

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.5%
EPSS 3.5% chance of exploitation in 30 days, percentile 89%
public exploits
0
none known

Summary

The mq_notify function in the GNU C Library (aka glibc) versions 2.32 and 2.33 has a use-after-free. It may use the notification thread attributes object (passed through its struct sigevent parameter) after it has been freed by the caller, leading to a denial of service (application crash) or possibly unspecified other impact.

Patch / fix

  • 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
  • glibc Debian 14, Debian 13, Debian 12 2.32-1

debian advisories DEBIAN-CVE-2021-33574

  • glibc RHEL 8 2.28-164.el8
  • nscd RHEL 8 2.28-164.el8
  • libnsl RHEL 8 2.28-164.el8
  • nss_db RHEL 8 2.28-164.el8
  • nss_hesiod RHEL 8 2.28-164.el8
  • glibc-utils RHEL 8 2.28-164.el8
  • glibc-common RHEL 8 2.28-164.el8
  • glibc-benchtests RHEL 8 2.28-164.el8

red hat advisories RHSA-2021:4358

  • glibc SLE Module for Development Tools 15 SP3, SLE Module for Basesystem 15 SP3, SLE Micro 5.1 2.31-9.3.2
  • glibc SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +10 more 2.26-13.59.1
  • glibc SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES 12 SP5 +4 more 2.22-114.15.1
  • glibc SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +4 more 2.22-116.1
  • glibc SLES 11 SP4-LTSS, SLE Point of Sale 11 SP3 2.11.3-17.110.37.1

suse advisories SUSE-SU-2021:3291-1SUSE-SU-2021:3385-1SUSE-SU-2021:3290-1SUSE-SU-2021:3289-1SUSE-SU-2021:14822-1

  • glibc openSUSE Tumbleweed 2.34-1.2
  • glibc openSUSE Leap 15.3 2.31-9.3.2
  • glibc openSUSE Leap 15.2 2.26-lp152.26.9.1
  • glibc-testsuite-src openSUSE Leap 15.2 2.26-lp152.26.9.1

opensuse advisories openSUSE-SU-2024:10792-1openSUSE-SU-2021:3291-1openSUSE-SU-2021:1374-1

  • nss_hesiod AlmaLinux 8 2.28-164.el8
  • glibc-utils AlmaLinux 8 2.28-164.el8
  • glibc-benchtests AlmaLinux 8 2.28-164.el8
  • compat-libpthread-nonshared AlmaLinux 8 2.28-164.el8

almalinux advisories ALSA-2021:4358

  • glibc Rocky Linux 8 2.28-164.el8

rocky linux advisories RLSA-2021:4358

  • glibc Arch Linux 2.34-1

arch linux advisories AVG-1621

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-2021-33574 updated cvss 5.9

glibc: mq_notify does not handle separately allocated thread attributes

  • Red Hat Enterprise Linux 6 nscd, glibc, glibc-utils, compat-glibc, glibc-common Red Hat Enterprise Linux 7 nscd, glibc, glibc-utils, compat-glibc, glibc-common
    affected: no fix planned “Out of support scope”
  • Red Hat CodeReady Linux Builder (v. 8) nss_hesiod 2.28-164.el8, glibc-benchtests 2.28-164.el8, glibc-debuginfo-common 2.28-164.el8 Red Hat Enterprise Linux AppStream (v. 8) glibc-utils 2.28-164.el8, glibc-debuginfo-common 2.28-164.el8, compat-libpthread-nonshared 2.28-164.el8 Red Hat Enterprise Linux BaseOS (v. 8) nscd 2.28-164.el8, glibc 2.28-164.el8, libnsl 2.28-164.el8, nss_db 2.28-164.el8, glibc-common 2.28-164.el8, glibc-all-langpacks 2.28-164.el8, +3 more
    fixed: vendor fix RHSA-2021:4358
  • Red Hat Enterprise Linux 9 nscd, glibc, libnsl, nss_db, nss_hesiod, glibc-utils, +6 more
    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 ICSA-23-166-10 updated cvss 9.8

Siemens SIMATIC S7-1500 TM MFP BIOS

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

Exploit prediction

3.52% chance of exploitation in the next 30 days, higher than 89% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • sourceware.org https://sourceware.org/bugzilla/show_bug.cgi?id=27896 referenced PoC, tagged "exploit" by a source, unverified

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

Affected products

  • 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.