CVE-2021-4138

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 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-4138 is rated Low Risk (39.6/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.77%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-4138

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.19% 0.77% +0.59%
2 2025-05-13 0.30% 0.19% -0.12%
3 2025-05-12 — 0.30% —

Full EPSS history (8 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-4138

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-4138

OS Trackers for CVE-2021-4138

vendor priority summary link
redhat medium — https://access.redhat.com/security/cve/CVE-2021-4138

Affected software / configurations for CVE-2021-4138

Vendor Product Version Raw CPE
mozilla geckodriver < 0.30.0 cpe:2.3:a:mozilla:geckodriver:*:*:*:*:*:*:*:*

References for CVE-2021-4138

URL Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=1652612 Issue Tracking Permissions Required Third Party Advisory
https://github.com/mozilla/geckodriver/releases/tag/v0.30.0 Release Notes Third Party Advisory
cvelogic Threat Intelligence