HOMEVULNERABILITIESCVE-2021-21707
MEDIUM

CVE-2021-21707

CWE-159Published: November 29, 2021· Updated: Jun 17, 2026

5.3
CVSS v3.1

Official Description

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.

NVD Source

Technical Analysis

CVE-2021-21707 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityLow
IntegrityNone
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected Vendors & Products

Debian1 product(s)
debian linux
netapp1 product(s)
clustered data ontap
PHP1 product(s)
php
tenable1 product(s)
tenable.sc
Source: NVD CPE · 5 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://bugs.php.net/bug.php?id=79971
PATCHhttps://www.tenable.com/security/tns-2022-09
PATCHhttps://bugs.php.net/bug.php?id=79971
PATCHhttps://www.tenable.com/security/tns-2022-09
ADVISORYhttps://security.netapp.com/advisory/ntap-20211223-0005/
ADVISORYhttps://www.debian.org/security/2022/dsa-5082
ADVISORYhttps://security.netapp.com/advisory/ntap-20211223-0005/
ADVISORYhttps://www.debian.org/security/2022/dsa-5082

All References (10)

→
https://bugs.php.net/bug.php?id=79971Exploit · Issue Tracking · Patch · Release Notes · Vendor Advisory
→
https://lists.debian.org/debian-lts-announce/2022/12/msg00030.htmlIssue Tracking · Mailing List
→
https://security.netapp.com/advisory/ntap-20211223-0005/Third Party Advisory
→
https://www.debian.org/security/2022/dsa-5082Third Party Advisory
→
https://www.tenable.com/security/tns-2022-09Patch · Release Notes · Third Party Advisory
→
https://bugs.php.net/bug.php?id=79971Exploit · Issue Tracking · Patch · Release Notes · Vendor Advisory
→
https://lists.debian.org/debian-lts-announce/2022/12/msg00030.htmlIssue Tracking · Mailing List
→
https://security.netapp.com/advisory/ntap-20211223-0005/Third Party Advisory
→
https://www.debian.org/security/2022/dsa-5082Third Party Advisory
→
https://www.tenable.com/security/tns-2022-09Patch · Release Notes · Third Party Advisory

Quick Facts

CVE IDCVE-2021-21707
CVSS Score5.3 / 10
SeverityMEDIUM
WeaknessCWE-159
CISA KEVNo
Affected4 vendor(s)
PublishedNov 29, 2021

Related CVEs (CWE-159)

CVE-2019-9505
9.8
CVE-2020-1646
7.5
CVE-2020-1648
7.5
CVE-2020-1653
7.5
CVE-2026-35536
7.2
CVE-2026-2636
5.5

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-21707 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
← All Vulnerabilities·Search for CVE-2021-21707·NVD