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CVE-2021-4138

20
FAUCET Score

CVE-2021-4138 addresses improved host header checks in mozilla geckodriver to prevent requests not directed at a known local hostname, IP, or the server's specified hostname. This vulnerability has a CVSS score of 5.3 (Medium), indicating a network-based attack with low complexity, requiring no privileges or user interaction, and potentially leading to low integrity impact. There is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 0.30.0CPE matchmatch criteria
cpe:2.3:a:mozilla:geckodriver:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.81%
Probability of exploitation in next 30 days
EPSS Percentile
53.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-26
Model: v2026.06.15
This CVE's current EPSS score of 0.0081 is in the 33rd percentile among its peer group of 23,701 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Advisories (1)

redhatCVE-2021-4138Moderate

geckodriver: DNS rebinding vulnerability

Sep 16, 2021

References

bugzilla.mozilla.org / show_bug.cgi
Issue TrackingPermissions RequiredThird Party Advisory
github.com / mozilla/geckodriver/releases/tag/v0.30.0
Release NotesThird Party Advisory