CVE-2021-3838Public exploitNetwork attack vector

Remote code execution via unchecked PHAR resource protocol

Published Nov 15, 2024 · Updated Nov 18, 2024

PHAR deserialization in dompdf before 2.0.0 allows remote attackers to execute code through an attacker-controlled resource URI. Resource-loading paths pass an insufficiently validated phar:// URI to file_get_contents(), causing PHP to deserialize an uploaded archive and instantiate arbitrary objects. Exploitation requires PHP before 8.0.0, control of rendered HTML, arbitrary file upload, and a usable PHP object-injection chain in the host application.

CVSS severity9.8
Critical
EPSS probability1.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

PHAR deserialization in dompdf before 2.0.0 allows remote attackers to execute code through an attacker-controlled resource URI. Resource-loading paths pass an insufficiently validated phar:// URI to file_get_contents(), causing PHP to deserialize an uploaded archive and instantiate arbitrary objects. Exploitation requires PHP before 8.0.0, control of rendered HTML, arbitrary file upload, and a usable PHP object-injection chain in the host application.

The record

CVE
CVE-2021-3838
Published
Nov 15, 2024
Updated
Nov 18, 2024
Vendor
dompdf
Product
dompdf
Classifications
CWE-502, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 15, 2024CVE publishedPublication date reported by the CVE source.
  2. Nov 18, 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=0 <2.0.0
  2. Affected versionversion=unspecified <2.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

dompdf · dompdfversion=0 <2.0.0; version=unspecified <2.0.0

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8Huntr CNACVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8CISA ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
T1190Exploit Public-Facing Application

Public exploit references

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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