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CVE-2021-21705

21
FAUCET Score

CVE-2021-21705 is a medium-severity vulnerability affecting PHP versions 7.3.x, 7.4.x, and 8.0.x, where the filter_var() function with FILTER_VALIDATE_URL incorrectly validates URLs containing an invalid password field. This flaw can lead to misinterpretation of URLs, potentially causing applications to connect to unintended servers or make incorrect access decisions. The vulnerability has a CVSS score of 5.3, indicating a network attack vector with low complexity and a low impact on integrity, but no impact on confidentiality or availability. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
>= 7.3.0, < 7.3.29CPE matchmatch criteria
cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
>= 7.4.0, < 7.4.21CPE matchmatch criteria
cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
>= 8.0.0, < 8.0.8CPE matchmatch criteria
cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:netapp:clustered_data_ontap:-:*:*:*:*:*:*:*
8.2CPE matchmatch criteria
cpe:2.3:a:oracle:sd-wan_aware:8.2:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

4.3MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.94%
Probability of exploitation in next 30 days
EPSS Percentile
78.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0194 is in the 66th percentile among its peer group of 23,705 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (6)

microsoftpatch availablevia msrc
Product: 19641-16823
microsoftpatch availablevia msrc
Product: cbl2 php on CBL Mariner 2.0
oraclepatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: php:7.4-8060020220120080432.0a326c83
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-php73-php-0:7.3.29-1.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-php73-php-0:7.3.29-1.el7
View patch

Vendor Advisories (2)

microsoft2021-Oct/CVE-2021-21705Moderate

Incorrect URL validation in FILTER_VALIDATE_URL

Oct 12, 2021
redhatCVE-2021-21705Moderate

php: SSRF bypass in FILTER_VALIDATE_URL

Jul 1, 2021

References

bugs.php.net / bug.php
ExploitIssue TrackingPatchVendor Advisory
security.gentoo.org / glsa/202209-20
Third Party Advisory
security.netapp.com / advisory/ntap-20211029-0006
Third Party Advisory
oracle.com / security-alerts/cpujan2022.html
PatchVendor Advisory