What’s Vulnerable › Vulnerabilities

CVE-2021-23985

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-03-31 · updated 2026-06-17

Description

If an attacker is able to alter specific about:config values (for example malware running on the user's computer), the Devtools remote debugging feature could have been enabled in a way that was unnoticable to the user. This would have allowed a remote attacker (able to make a direct network connection to the victim) to monitor the user's browsing activity and (plaintext) network traffic. This was addressed by providing a visual cue when Devtools has an open network socket. This vulnerability affects Firefox < 87.

Affected products

• Mozilla Firefox: before 87.0 — fixed in 87.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 87.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1659129
• https://www.mozilla.org/security/advisories/mfsa2021-10/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1659129
• https://www.mozilla.org/security/advisories/mfsa2021-10/

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