CVE-2021-21706Network attack vector

File overwrite via leading-slash ZIP paths

Published Oct 4, 2021 · Updated Sep 16, 2024

Path traversal in PHP 7.3.x before 7.3.31, 7.4.x before 7.4.24, and 8.0.x before 8.0.11 allows attackers to write Windows files. The php_zip_make_relative_path() helper strips the leading slash from a Windows current-volume path, leaving traversal segments that extractTo() resolves beyond the destination. Exploitation requires affected PHP code to extract a crafted ZIP archive, and file creation or overwrite remains limited by the PHP process permissions.

CVSS severity5.3
Medium
EPSS probability1.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in PHP 7.3.x before 7.3.31, 7.4.x before 7.4.24, and 8.0.x before 8.0.11 allows attackers to write Windows files. The php_zip_make_relative_path() helper strips the leading slash from a Windows current-volume path, leaving traversal segments that extractTo() resolves beyond the destination. Exploitation requires affected PHP code to extract a crafted ZIP archive, and file creation or overwrite remains limited by the PHP process permissions.

The record

CVE
CVE-2021-21706
Published
Oct 4, 2021
Updated
Sep 16, 2024
Vendor
The PHP Group
Product
PHP
Classifications
CWE-24, CWE-22, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 4, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=7.3.x <7.3.31
  2. Affected versionversion=7.4.x <7.4.24
  3. Affected versionversion=8.0.X <8.0.11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The PHP Group · PHPversion=7.3.x <7.3.31; version=7.4.x <7.4.24; version=8.0.X <8.0.11

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
5.3PHP GroupCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-24Path Traversal: '../filedir'
CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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