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CVE Record

CVE-2021-29987: After requesting multiple permissions, and closing the first permission panel, subsequent permission panels...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

On Linux, older Firefox and Thunderbird could show permission prompts in one place while still registering clicks as if the prompt were in its original position. A malicious site or content flow could trick a user into approving a permission they meant to deny or avoid.

Executive priority

Treat this as a moderate desktop risk, not an emergency server incident. It can lead to unintended permission grants, but sources limit impact to Linux and do not show active exploitation. Remediate through normal browser and mail client update channels.

Technical view

CVE-2021-29987 is a Linux-only Mozilla UI permission handling flaw affecting Firefox before 91 and Thunderbird before 91. After multiple permission requests, closing the first permission panel could reposition later panels while click handling remained tied to the default location, enabling unintended permission acceptance.

Likely exposure

Exposure is limited to Linux systems running Firefox < 91 or Thunderbird < 91. The provided CVE text says other operating systems are unaffected. Organizations with managed Linux desktops, developer workstations, kiosks, or legacy distro packages should check versions.

Exploitation context

The source bundle does not cite active exploitation, and the CVE is not listed as KEV. Practical exploitation would require user interaction with permission prompts. The impact depends on which permission is granted and how the target application is used.

Researcher notes

This is a permission prompt UI desynchronization issue, similar in risk shape to clickjacking or permission confusion. The public evidence provided does not include CVSS, CWE, exploit maturity, or detailed permission-specific impact, so validation should stay focused on version and Linux platform exposure.

Mitigation direction

  • Upgrade Firefox to version 91 or later on Linux systems.
  • Upgrade Thunderbird to version 91 or later on Linux systems.
  • Check Mozilla and Linux distribution advisories for package-specific guidance.
  • Prioritize managed Linux desktops and shared workstation environments.

Validation and detection

  • Inventory Linux hosts for installed Firefox and Thunderbird versions.
  • Confirm no Linux endpoint runs Firefox or Thunderbird below 91.
  • Review software management records for Mozilla package update coverage.
  • Verify non-Linux systems are not incorrectly flagged as affected.
Prepared
Confidence
high
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-29987 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
5Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefoxunspecifiedListed
MozillaThunderbirdunspecifiedListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.