Security readout for executives and security teams
Plain-English summary
Some PHP versions could incorrectly accept malformed URLs as valid. If an application used PHP’s URL validation as a security gate, it might contact an unintended server or make the wrong access decision. The issue is medium severity and depends heavily on how an application uses URL validation.
Executive priority
Prioritize remediation for internet-facing PHP services that process user-provided URLs or make automated outbound requests. Routine patching is appropriate where URL validation is not security-sensitive.
Technical view
CVE-2021-21705 is a CWE-20 input validation flaw in PHP filter_var() with FILTER_VALIDATE_URL. PHP 7.3.x before 7.3.29, 7.4.x before 7.4.21, and 8.0.x before 8.0.8 may accept a URL with an invalid password field as valid.
Likely exposure
Exposure is most likely in PHP applications or products running affected PHP versions and relying on FILTER_VALIDATE_URL for user-supplied URL trust, routing, allowlisting, redirects, or outbound connection decisions.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. Practical risk requires application logic that accepts attacker-controlled URLs and treats PHP validation as enough to make a sensitive access or connection decision.
Researcher notes
The CVSS vector is AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N, score 4.3. Impact is primarily secondary: incorrect URL acceptance can cause misrouting or mistaken trust decisions, but the bundle does not establish a universal direct compromise path.
Mitigation direction
- Upgrade PHP to 7.3.29, 7.4.21, 8.0.8, or a supported fixed release.
- Check vendor advisories for products bundling PHP, including listed Oracle, NetApp, and Gentoo sources.
- Avoid using FILTER_VALIDATE_URL alone for security-sensitive allowlisting or access decisions.
- Add application-level hostname, scheme, and destination checks where URL trust matters.
Validation and detection
- Inventory PHP runtime versions across applications, containers, and vendor appliances.
- Review code paths using filter_var() with FILTER_VALIDATE_URL on user-controlled input.
- Confirm URL validation is not the only control before outbound requests or access decisions.
- Run regression tests for malformed URL handling in affected business workflows.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CWE-20: Exact CWE lookup
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Open ATT&CK lookupCredential and access behavior lookup
The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-21705 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://bugs.php.net/bug.php?id=81122CVE reference · x_refsource_MISC
- https://www.oracle.com/security-alerts/cpujan2022.htmlCVE reference · x_refsource_MISC
- https://security.netapp.com/advisory/ntap-20211029-0006/CVE reference · x_refsource_CONFIRM
- GLSA-202209-20CVE reference · vendor-advisory, x_refsource_GENTOO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.