CVE-2021-29987

What it is

After requesting multiple permissions, and closing the first permission panel, subsequent permission panels will be displayed in a different position but still record a click in the default location, making it possible to trick a user into accepting a permission they did not want to. *This bug only affects Firefox on Linux. Other operating systems are unaffected.*. This vulnerability affects Firefox < 91 and Thunderbird < 91.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of data exposure.

Exploit odds

0.9% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-08-17 20:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:48 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.9% in the next 30 days (EPSS).
• Severity: 6.5 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-08-17 20:15 UTC

Last modified

2026-06-17 03:48 UTC

Exploit probability

0.9% · EPSS, next 30 days

Weakness

CWE-307

Record status

Modified

Affected

• Mozilla Firefox < 91.0
• Mozilla Thunderbird < 91.0

Attack profile CVSS 3.1 · 6.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-29987.md and follow it. Check whether this project is affected by CVE-2021-29987. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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