Security readout for executives and security teams
Plain-English summary
Some PHP XML file-loading functions could misunderstand a filename containing an encoded NUL character. In affected PHP versions, this could make an application read a different file than intended. Business risk is mainly unintended information disclosure, especially where applications accept or construct XML file paths from user-controlled input.
Executive priority
Treat as a moderate patching and exposure-review item, not an emergency absent exploitation evidence. Prioritize internet-facing PHP applications and systems where XML file paths may be influenced by users or external integrations.
Technical view
CVE-2021-21707 affects PHP 7.3.x before 7.3.33, 7.4.x before 7.4.26, and 8.0.x before 8.0.13. Certain XML parsing functions, including simplexml_load_file(), URL-decode filenames, and encoded NUL characters may truncate path interpretation. CVSS is 5.3, network reachable, low complexity, confidentiality impact only.
Likely exposure
Exposure is most likely in PHP applications running affected versions that call XML file-loading APIs with filenames influenced by users, requests, imports, or integrations. Internet-facing services are more relevant because the CVSS vector requires no privileges or user interaction.
Exploitation context
The bundle does not show CISA KEV listing or cited evidence of active exploitation. The described condition is remotely reachable in principle when an application exposes attacker-influenced XML filename handling, but exploitability depends on application path construction and file access context.
Researcher notes
The core issue is filename interpretation mismatch after URL decoding and NUL handling inside PHP XML parsing functions. Validate exposure at the application boundary: whether attacker-controlled data can reach affected file-loading APIs, and whether alternate file reads could disclose sensitive data.
Mitigation direction
- Upgrade PHP to 7.3.33, 7.4.26, 8.0.13, or later supported vendor packages.
- Apply Debian, distribution, appliance, or vendor security updates where PHP is bundled.
- Audit XML file-loading paths that accept user, URL, import, or integration-controlled filenames.
- Avoid passing untrusted filenames directly to XML parsing file APIs.
- Check vendor guidance for NetApp or other packaged products using embedded PHP.
Validation and detection
- Inventory PHP runtime versions across servers, containers, CI images, and appliances.
- Search code for simplexml_load_file() and similar XML file-loading calls.
- Confirm affected calls cannot receive user-controlled or URL-decoded filenames.
- Verify deployed packages include Debian DSA-5082 or equivalent vendor fixes.
- Review access logs for unusual XML file path inputs where applicable.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-159: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-21707 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
- 5.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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:N/S:U/C:L/I:N/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://bugs.php.net/bug.php?id=79971CVE reference
- https://security.netapp.com/advisory/ntap-20211223-0005/CVE reference
- DSA-5082CVE reference · vendor-advisory
- https://www.tenable.com/security/tns-2022-09CVE reference
- [debian-lts-announce] 20221215 [SECURITY] [DLA 3243-1] php7.3 security updateCVE reference · mailing-list
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 Handling of Invalid Use of Special Elements
Improper Handling of Invalid Use of Special Elements represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.