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Fencer Vulns
medium 5.3

CVE-2021-4138 json

Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.

published 2022-05-02 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-34008

cvss
5.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 58%
public exploits
0
none known

Summary

Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.

Patch / fix

  • Mozilla geckodriver 0.30.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-4138 updated cvss 7.5

geckodriver: DNS rebinding vulnerability

  • Red Hat Advanced Cluster Management for Kubernetes 2 geckodriver
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.85% chance of exploitation in the next 30 days, higher than 58% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N

Affected products

  • Mozilla geckodriver

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.