CVE-2021-21707
MEDIUMEPSS 98th pctlDescription
In PHP versions 7.3.x below 7.3.33, 7.4.x below 7.4.26 and 8.0.x below 8.0.13, certain XML parsing functions, like simplexml_load_file(), URL-decode the filename passed to them. If that filename contains URL-encoded NUL character, this may cause the function to interpret this as the end of the filename, thus interpreting the filename differently from what the user intended, which may lead it to reading a different file than intended.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Exploit Intelligence
Very high risk: more likely to be exploited than 98% of all known CVEs.
References
Related Vulnerabilities
Other CWE-159 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2019-9505 | Critical | 9.8 | 3.5% | - | - |
| CVE-2020-1653 | High | 7.5 | 1.6% | - | - |
| CVE-2020-1648 | High | 7.5 | 1.3% | - | - |
| CVE-2020-1646 | High | 7.5 | 1.0% | - | - |
| CVE-2020-29022 | Medium | 5.3 | 0.8% | - | Fix |
| CVE-2026-2636 | Medium | 5.5 | 0.4% | - | - |
Common questions
How do I fix CVE-2021-21707?
Published advisories record a fix for 13 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2021-21707 being actively exploited?
Not that we know of. CVE-2021-21707 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 26.0% is the estimated probability that it will be exploited in the next 30 days. That is higher than 98% of all scored CVEs.
How severe is CVE-2021-21707?
CVE-2021-21707 has a CVSS v3 base score of 5.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-21707 affect?
Published advisories record a fix for php7.4 (Debian), php7.0 (Ubuntu), php7.0-cgi (Ubuntu), php7.0-cli (Ubuntu), and 9 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.