What’s Vulnerable › Vulnerabilities

CVE-2021-4138

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2022-05-02 · updated 2026-06-17

Description

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

Affected products

• Mozilla geckodriver: before 0.30.0 — fixed in 0.30.0

How to fix

Upgrade to a fixed version: Mozilla geckodriver 0.30.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1652612
• https://github.com/mozilla/geckodriver/releases/tag/v0.30.0
• https://bugzilla.mozilla.org/show_bug.cgi?id=1652612
• https://github.com/mozilla/geckodriver/releases/tag/v0.30.0

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