Skip to content
Fencer Vulns
high 7.8

CVE-2021-21703 json

PHP-FPM memory access in root process leading to privilege escalation

published 2021-10-25 5 y ago modified 2026-09-08 2 mo ago also BIT-libphp-2021-21703 , BIT-php-2021-21703 , BIT-php-min-2021-21703 , EUVD-2021-8875

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.4%
EPSS 1.4% chance of exploitation in 30 days, percentile 73%
public exploits
0
none known

Summary

In PHP versions 7.3.x up to and including 7.3.31, 7.4.x below 7.4.25 and 8.0.x below 8.0.12, when running PHP FPM SAPI with main FPM daemon process running as root and child worker processes running as lower-privileged users, it is possible for the child processes to access memory shared with the main process and write to it, modifying it in a way that would cause the root process to conduct invalid memory reads and writes, which can be used to escalate privileges from local unprivileged user to the root user.

Patch / fix

  • bitnami libphp 7.3.32, 7.4.25, 8.0.12
  • bitnami php 7.3.32, 7.4.25, 8.0.12
  • bitnami php-min 7.3.32, 7.4.25, 8.0.12
  • PHP Group PHP 7.4.25, 8.0.12
  • php7.4 Debian 11 7.4.25-1+deb11u1

debian advisories DEBIAN-CVE-2021-21703

  • php7.2 Ubuntu 18.04 LTS 7.2.24-0ubuntu0.18.04.10
  • php7.4 Ubuntu 20.04 LTS 7.4.3-4ubuntu2.7
  • php5 Ubuntu Pro 14.04 LTS 5.5.9+dfsg-1ubuntu4.29+esm15
  • php7.0 Ubuntu Pro 16.04 LTS 7.0.33-0ubuntu0.16.04.16+esm2

ubuntu advisories UBUNTU-CVE-2021-21703

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

  • php RHEL 8 7.4.19-2.module+el8.6.0+13953+0a59ce9f
  • libzip RHEL 8 1.6.1-1.module+el8.3.0+6678+b09f589e
  • php-gd RHEL 8 7.4.19-2.module+el8.6.0+13953+0a59ce9f
  • php-cli RHEL 8 7.4.19-2.module+el8.6.0+13953+0a59ce9f
  • php-dba RHEL 8 7.4.19-2.module+el8.6.0+13953+0a59ce9f
  • php-dbg RHEL 8 7.4.19-2.module+el8.6.0+13953+0a59ce9f
  • php-ffi RHEL 8 7.4.19-2.module+el8.6.0+13953+0a59ce9f
  • php-fpm RHEL 8 7.4.19-2.module+el8.6.0+13953+0a59ce9f

red hat advisories RHSA-2022:1935RHSA-2022:5491

  • php7 SLES for SAP 15 SP2, SLES 15 SP2-LTSS, SLES 15 SP2-BCL +10 more 7.4.33-150200.3.46.2
  • php7-test openSUSE Leap 15.3 7.4.33-150200.3.46.2
  • php74 SLE Software Development Kit 12 SP5, SLE Module for Web and Scripting 12 7.4.33-1.47.2
  • php7 SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +8 more 7.2.34-150000.4.103.1
  • php8 SLE Module for Web and Scripting 15 SP4, openSUSE Leap 15.4 8.0.24-150400.4.14.1
  • php8-fpm SLE Module for Web and Scripting 15 SP4, openSUSE Leap 15.4 8.0.24-150400.4.14.1
  • php8-test SLE Module for Web and Scripting 15 SP4, openSUSE Leap 15.4 8.0.24-150400.4.14.1
  • php8-embed SLE Module for Web and Scripting 15 SP4, openSUSE Leap 15.4 8.0.24-150400.4.14.1

suse advisories SUSE-SU-2022:4069-1SUSE-SU-2022:4068-1SUSE-SU-2022:4067-1SUSE-SU-2022:3661-1SUSE-SU-2022:0679-1SUSE-SU-2021:3943-1

  • php8 openSUSE Tumbleweed 8.0.12-1.1
  • php7 openSUSE Tumbleweed 7.4.25-1.1
  • php7 openSUSE Leap 15.2 7.4.6-lp152.2.21.1
  • php7-test openSUSE Leap 15.2 7.4.6-lp152.2.21.1
  • php7 openSUSE Leap 15.3 7.4.6-3.29.1
  • php7-test openSUSE Leap 15.3 7.4.6-3.29.1

opensuse advisories openSUSE-SU-2024:11585-1openSUSE-SU-2024:11594-1openSUSE-SU-2021:1570-1openSUSE-SU-2021:3943-1

  • php AlmaLinux 8 7.4.19-2.module_el8.6.0+2750+78feabcb
  • libzip AlmaLinux 8 1.6.1-1.module_el8.6.0+2750+78feabcb
  • php-gd AlmaLinux 8 7.4.19-2.module_el8.6.0+2750+78feabcb
  • php-cli AlmaLinux 8 7.4.19-2.module_el8.6.0+2750+78feabcb
  • php-dba AlmaLinux 8 7.4.19-2.module_el8.6.0+2750+78feabcb
  • php-dbg AlmaLinux 8 7.4.19-2.module_el8.6.0+2750+78feabcb
  • php-ffi AlmaLinux 8 7.4.19-2.module_el8.6.0+2750+78feabcb
  • php-fpm AlmaLinux 8 7.4.19-2.module_el8.6.0+2750+78feabcb

almalinux advisories ALSA-2022:1935

  • php Rocky Linux 8 7.4.19-2.module+el8.6.0+789+2130c178
  • libzip Rocky Linux 8 1.6.1-1.module+el8.6.0+789+2130c178
  • libzip Rocky Linux 8 1.6.1-1.module+el8.4.0+415+e936cba3
  • php-pear Rocky Linux 8 1:1.10.12-1.module+el8.4.0+415+e936cba3
  • php-pear Rocky Linux 8 1:1.10.12-1.module+el8.6.0+789+2130c178
  • php-pecl-rrd Rocky Linux 8 2.0.1-1.module+el8.4.0+414+2e7afcdd
  • php-pecl-zip Rocky Linux 8 1.18.2-1.module+el8.6.0+789+2130c178
  • php-pecl-zip Rocky Linux 8 1.18.2-1.module+el8.4.0+415+e936cba3

rocky linux advisories RLSA-2022:1935

  • php7 Alpine 3.12 7.3.32-r0
  • php7 Alpine 3.15, Alpine 3.14, Alpine 3.13 7.4.25-r0
  • php8 Alpine 3.16, Alpine 3.15, Alpine 3.14 +1 more 8.0.12-r0
  • php81 Alpine 3.19, Alpine 3.18, Alpine 3.17 +1 more 8.1.0_rc5-r0

alpine advisories ALPINE-CVE-2021-21703

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

  • php Arch Linux 8.0.12-1

arch linux advisories AVG-2486

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-2021-21703 updated cvss 6.4

php: Local privilege escalation via PHP-FPM

  • Red Hat Enterprise Linux 6 php, php-gd, php-cli, php-dba, php-fpm, php-pdo, +20 more Red Hat Enterprise Linux 7 php, php-gd, php-cli, php-dba, php-fpm, php-pdo, +18 more Red Hat Enterprise Linux 8 php, libzip, php-gd, php-cli, php-dba, php-dbg, +30 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) php 7.4.19-2.module+el8.6.0+13953+0a59ce9f, libzip 1.6.1-1.module+el8.3.0+6678+b09f589e, php-gd 7.4.19-2.module+el8.6.0+13953+0a59ce9f, php-cli 7.4.19-2.module+el8.6.0+13953+0a59ce9f, php-dba 7.4.19-2.module+el8.6.0+13953+0a59ce9f, php-dbg 7.4.19-2.module+el8.6.0+13953+0a59ce9f, +28 more
    fixed: vendor fix RHSA-2022:1935
  • Red Hat Software Collections for RHEL Workstation(v. 7) rh-php73-php 7.3.33-1.el7, rh-php73-php-gd 7.3.33-1.el7, rh-php73-php-cli 7.3.33-1.el7, rh-php73-php-dba 7.3.33-1.el7, rh-php73-php-dbg 7.3.33-1.el7, rh-php73-php-fpm 7.3.33-1.el7, +22 more Red Hat Software Collections for RHEL(v. 7) rh-php73-php 7.3.33-1.el7, rh-php73-php-gd 7.3.33-1.el7, rh-php73-php-cli 7.3.33-1.el7, rh-php73-php-dba 7.3.33-1.el7, rh-php73-php-dbg 7.3.33-1.el7, rh-php73-php-fpm 7.3.33-1.el7, +22 more
    fixed: vendor fix RHSA-2022:5491
  • Red Hat Enterprise Linux 9 php, php-gd, php-cli, php-dba, php-dbg, php-ffi, +18 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-26-027-02 updated cvss 7.0

Festo Didactic SE MES PC

  • Festo Didactic SE MES PC shipped_with_Windows_10
    affected: vendor fix

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

Exploit prediction

1.43% chance of exploitation in the next 30 days, higher than 73% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugs.php.net https://bugs.php.net/bug.php?id=81026 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD 3.1 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 6.9 AV:L/AC:M/Au:N/C:C/I:C/A:C
OSV 3.1 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
bitnami libphp
>=7.3.0, <7.3.32
>=7.4.0, <7.4.25
>=8.0.0, <8.0.12
7.3.32
7.4.25
8.0.12
bitnami php
>=7.3.0, <7.3.32
>=7.4.0, <7.4.25
>=8.0.0, <8.0.12
7.3.32
7.4.25
8.0.12
bitnami php-min
>=7.3.0, <7.3.32
>=7.4.0, <7.4.25
>=8.0.0, <8.0.12
7.3.32
7.4.25
8.0.12

Affected products

  • PHP Group PHP

Classification

Weakness
Technology feeds

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.