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Fencer Vulns
medium 4.3

CVE-2021-21705 json

Incorrect URL validation in FILTER_VALIDATE_URL

published 2021-10-04 5 y ago modified 2026-09-08 2 mo ago also BIT-libphp-2021-21705 , BIT-php-2021-21705 , BIT-php-min-2021-21705 , EUVD-2021-8877

cvss
4.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.1%
EPSS 2.1% chance of exploitation in 30 days, percentile 81%
public exploits
0
none known

Summary

In PHP versions 7.3.x below 7.3.29, 7.4.x below 7.4.21 and 8.0.x below 8.0.8, when using URL validation functionality via filter_var() function with FILTER_VALIDATE_URL parameter, an URL with invalid password field can be accepted as valid. This can lead to the code incorrectly parsing the URL and potentially leading to other security implications - like contacting a wrong server or making a wrong access decision.

Patch / fix

  • bitnami libphp 7.3.29, 7.4.21, 8.0.8
  • bitnami php 7.3.29, 7.4.21, 8.0.8
  • bitnami php-min 7.3.29, 7.4.21, 8.0.8
  • PHP Group PHP 7.3.29, 7.4.21, 8.0.8
  • php7.4 Debian 11 7.4.21-1+deb11u1

debian advisories DEBIAN-CVE-2021-21705

  • php7.2 Ubuntu 18.04 LTS 7.2.24-0ubuntu0.18.04.8
  • php7.4 Ubuntu 20.04 LTS 7.4.3-4ubuntu2.5
  • php5 Ubuntu Pro 14.04 LTS 5.5.9+dfsg-1ubuntu4.29+esm14
  • php7.0 Ubuntu Pro 16.04 LTS 7.0.33-0ubuntu0.16.04.16+esm1

ubuntu advisories UBUNTU-CVE-2021-21705

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-2021:2992

  • 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
  • php7 SLE Module for Web and Scripting 15 SP3, SLE Module for Web and Scripting 15 SP2, SLE Module for Package Hub 15 SP3 +1 more 7.4.6-3.22.1
  • php74 SLE Software Development Kit 12 SP5, SLE Module for Web and Scripting 12 7.4.6-1.24.1
  • php72 SLE Software Development Kit 12 SP5, SLE Module for Web and Scripting 12 7.2.5-1.63.2

suse advisories SUSE-SU-2022:4069-1SUSE-SU-2022:4068-1SUSE-SU-2022:4067-1SUSE-SU-2021:2637-1SUSE-SU-2021:2636-1SUSE-SU-2021:2564-1

  • php7 openSUSE Leap 15.2 7.4.6-lp152.2.18.1
  • php7-test openSUSE Leap 15.2 7.4.6-lp152.2.18.1
  • php7 openSUSE Leap 15.3 7.4.6-3.22.1
  • php7 openSUSE Leap 15.3 7.2.5-4.76.5

opensuse advisories openSUSE-SU-2021:1130-1openSUSE-SU-2021:2637-1openSUSE-SU-2021:2575-1

  • 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 7.3.29-r0
  • php7 Alpine 3.15, Alpine 3.14, Alpine 3.13 7.4.21-r0
  • php8 Alpine 3.16, Alpine 3.15, Alpine 3.14 +1 more 8.0.8-r0

alpine advisories ALPINE-CVE-2021-21705

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 8.0.8-1

arch linux advisories AVG-2132

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-2021-21705 updated cvss 5.3

php: SSRF bypass in FILTER_VALIDATE_URL

  • 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 Red Hat Enterprise Linux Server (v. 7) rh-php73-php 7.3.29-1.el7, rh-php73-php-gd 7.3.29-1.el7, rh-php73-php-cli 7.3.29-1.el7, rh-php73-php-dba 7.3.29-1.el7, rh-php73-php-dbg 7.3.29-1.el7, rh-php73-php-fpm 7.3.29-1.el7, +22 more Red Hat Software Collections for Red Hat Enterprise Linux Server EUS (v. 7.7) rh-php73-php 7.3.29-1.el7, rh-php73-php-gd 7.3.29-1.el7, rh-php73-php-cli 7.3.29-1.el7, rh-php73-php-dba 7.3.29-1.el7, rh-php73-php-dbg 7.3.29-1.el7, rh-php73-php-fpm 7.3.29-1.el7, +22 more Red Hat Software Collections for Red Hat Enterprise Linux Workstation (v. 7) rh-php73-php 7.3.29-1.el7, rh-php73-php-gd 7.3.29-1.el7, rh-php73-php-cli 7.3.29-1.el7, rh-php73-php-dba 7.3.29-1.el7, rh-php73-php-dbg 7.3.29-1.el7, rh-php73-php-fpm 7.3.29-1.el7, +22 more
    fixed: vendor fix RHSA-2021:2992
  • 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 5.3

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

2.09% chance of exploitation in the next 30 days, higher than 81% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugs.php.net https://bugs.php.net/bug.php?id=81122 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N
OSV 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
bitnami libphp
>=7.3.0, <7.3.29
>=7.4.0, <7.4.21
>=8.0.0, <8.0.8
7.3.29
7.4.21
8.0.8
bitnami php
>=7.3.0, <7.3.29
>=7.4.0, <7.4.21
>=8.0.0, <8.0.8
7.3.29
7.4.21
8.0.8
bitnami php-min
>=7.3.0, <7.3.29
>=7.4.0, <7.4.21
>=8.0.0, <8.0.8
7.3.29
7.4.21
8.0.8

Affected products

  • PHP Group PHP

Classification

Weakness
  • CWE-20 Improper Input Validation
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.