CVE-2021-4138
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or...
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
NVD Score used
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.
- Record
CVE-2021-4138- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - CVSS 2.0
- 5.0 Medium
AV:N/AC:L/Au:N/C:N/I:P/A:N - Updated
- 2026-11-02
CVE List No score
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.
- Record
CVE-2021-4138- Updated
- 2026-11-02
EUVDEUVD-2021-34008 No score
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.
- Record
EUVD-2021-34008- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-2h28-m3qw-8www
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or...
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.
- Record
GHSA-2h28-m3qw-8www- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-02
OSV
Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.
- Record
CVE-2021-4138- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-02
Affected products
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-4138 is a medium vulnerability (CVSS 5.3) in Mozilla Geckodriver, published May 2, 2022. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.85%, the 58th percentile. No source names a fixed version.