CVE-2021-21705 | Incorrect URL validation in FILTER_VALIDATE_URL

Exp

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.

Published: 2021-10-04 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-21705 is rated High Exploit Risk (61.2/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 2.00%). 1 public exploit reference(s) are indexed (Exploit-DB). EPSS rose +1.71% over the last day, indicating growing attacker interest. Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-21705

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-21705

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.29% 2.00% +1.71%
2 2026-03-04 0.08% 0.29% +0.21%
3 2026-03-01 — 0.08% —

Full EPSS history (38 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-21705

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 1.4 [email protected]
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-21705

OS Trackers for CVE-2021-21705

vendor priority summary link
alpine medium CVE-2021-21705: 2 source package rows (php7, php8); 2 state rows across 1 repos (edge-community); fixed 2, open 0. https://security.alpinelinux.org/vuln/CVE-2021-21705
debian not yet assigned CVE-2021-21705 not yet assigned priority: Debian including 1 source packages (php7.4), 1 status rows across 1 suites (bullseye): resolved 1. https://security-tracker.debian.org/tracker/CVE-2021-21705
gentoo high CVE-2021-21705: 1 GLSA(s) (202209-20), 1 atom(s) (dev-lang/php); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-21705
redhat medium — https://access.redhat.com/security/cve/CVE-2021-21705
suse medium CVE-2021-21705 severity moderate: SUSE including 705 source package names (apache2-mod_php5-5.2.14-111.80.1, apache2-mod_php53-5.3.17-112.102.2, …), 1781 product×package rows across 42 product lines (SUSE CaaS Platform 4.0, SUSE Enterprise Storage 6, … (42 product lines)): Fixed 1684, Known Not Affected 97. https://www.suse.com/security/cve/CVE-2021-21705/
ubuntu medium CVE-2021-21705 medium priority: Ubuntu including 6 source packages (php5, php7.0, php7.2, php7.4, php8.0, php8.1), 54 status rows across 9 suites (bionic, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): DNE 40, released 9, needs-triage 4, not-affected 1. https://ubuntu.com/security/CVE-2021-21705

Affected software / configurations for CVE-2021-21705

Vendor Product Version Raw CPE
php php >= 7.3.0, < 7.3.29 cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
php php >= 7.4.0, < 7.4.21 cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
php php >= 8.0.0, < 8.0.8 cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
netapp clustered_data_ontap — cpe:2.3:a:netapp:clustered_data_ontap:-:*:*:*:*:*:*:*
oracle sd-wan_aware 8.2 cpe:2.3:a:oracle:sd-wan_aware:8.2:*:*:*:*:*:*:*

References for CVE-2021-21705

cvelogic Threat Intelligence