How severe is CVE-2021-21705?

CVE-2021-21705 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2021-21705 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21705?

CVE-2021-21705 primarily affects Php. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-21705?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-21705 published?

CVE-2021-21705 was published on 2021-10-04 and last updated on 2026-06-17.

CVE-2021-21705

CVE-2021-21705 is a medium-severity vulnerability in Php with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
CVSS v2: 5.0
EPSS exploit prediction: 2% (78th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Php
Published: 2021-10-04
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-21705?: 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.
How severe is CVE-2021-21705?: CVE-2021-21705 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2021-21705 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21705?: CVE-2021-21705 primarily affects Php. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-21705?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-21705 published?: CVE-2021-21705 was published on 2021-10-04 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
cpe:2.3:a:netapp:clustered_data_ontap:-:*:*:*:*:*:*:*
cpe:2.3:a:oracle:sd-wan_aware:8.2:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

223.197.186.7 (ipv4-addr)
20.157.117.15 (ipv4-addr)
34.83.189.112 (ipv4-addr)
220.178.39.106 (ipv4-addr)
103.174.34.49 (ipv4-addr)
61.7.144.60 (ipv4-addr)
49.0.82.4 (ipv4-addr)
221.228.203.3 (ipv4-addr)