CVE-2021-4138Public exploitNetwork attack vector

Remote code execution via DNS-rebound WebDriver requests

Published May 2, 2022 · Updated Aug 3, 2024

DNS rebinding in Mozilla geckodriver before 0.30.0 allows remote attackers to execute code through requests from a malicious origin. The WebDriver HTTP server accepts a rebound hostname because it does not validate the Host header against local or server-specified names. Exploitation requires browser-loaded attacker content and a reachable geckodriver listener; success permits session control, local-file reads, and program execution with geckodriver privileges.

CVSS severity5.3
Medium
EPSS probability0.83%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

DNS rebinding in Mozilla geckodriver before 0.30.0 allows remote attackers to execute code through requests from a malicious origin. The WebDriver HTTP server accepts a rebound hostname because it does not validate the Host header against local or server-specified names. Exploitation requires browser-loaded attacker content and a reachable geckodriver listener; success permits session control, local-file reads, and program execution with geckodriver privileges.

The record

CVE
CVE-2021-4138
Published
May 2, 2022
Updated
Aug 3, 2024
Vendor
Mozilla
Product
geckodriver
Classifications
CWE-20, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 2, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=unspecified <0.30.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · geckodriverversion=unspecified <0.30.0

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/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 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-20Improper Input Validation
T1189Drive-by Compromise

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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