What’s Vulnerable › Vulnerabilities

CVE-2021-21705: Incorrect URL validation in FILTER_VALIDATE_URL

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.1% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-10-04 · updated 2026-06-17
• Weakness: CWE-20

Description

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.

Affected products

• Clustered Data ONTAP: all versions
• Oracle Corporation SD-WAN Aware: 8.2
• PHP: from 7.3.0 before 7.3.29; from 7.4.0 before 7.4.21; from 8.0.0 before 8.0.8 — fixed in 7.3.29, 7.4.21, 8.0.8

How to fix

Upgrade to a fixed version: PHP 7.3.29, 7.4.21, 8.0.8. Check the vendor advisory for mitigations.

References

• https://bugs.php.net/bug.php?id=81122
• https://security.gentoo.org/glsa/202209-20
• https://security.netapp.com/advisory/ntap-20211029-0006/
• https://www.oracle.com/security-alerts/cpujan2022.html
• https://bugs.php.net/bug.php?id=81122
• https://security.gentoo.org/glsa/202209-20
• https://security.netapp.com/advisory/ntap-20211029-0006/
• https://www.oracle.com/security-alerts/cpujan2022.html

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