CVE intelligence and bounded remediation

CVE-2021-43538 — Mozilla Firefox security vulnerability

Medium CVSS 4.3

By misusing a race in our notification code, an attacker could have forcefully hidden the notification for pages that had received full screen and pointer lock access, which could have been used for spoofing attacks. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

Severity
Medium
CVSS
4.3 (3.1)
Published
2021-12-08
CISA KEV
Not currently listed
Ecosystem
browser
Weaknesses
CWE-362

Affected products

  • mozilla / firefox
  • mozilla / firefox_esr
  • mozilla / thunderbird
  • debian / debian_linux / 9.0
  • debian / debian_linux / 10.0
  • debian / debian_linux / 11.0

Matched remediation archetype

Race condition, TOCTOU, and lifecycle synchronization

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

  • Map concurrent actors, shared state, lock boundaries, signals, callbacks, retries, and check-then-use sequences in the affected path.
  • Determine whether untrusted users can influence timing, object names, filesystem state, or repeated state transitions.
  • Identify clustered and multi-process behavior that repository-local tests may not represent.

Remediate safely

  • Make the sensitive state transition atomic or protect it with a consistently ordered synchronization primitive.
  • Perform authorization and invariant checks on the same authoritative object and transaction used for the operation.
  • Use unique private resources, safe ownership transfer, and idempotent operations; add deterministic concurrency regression tests.

Authoritative sources

Complete CVE record and remediation plan

The detailed catalog view below loads this exact record, its source evidence, and the full seven-phase agentic change plan.