Actively exploited in the wild
Mozilla Firefox And Thunderbird Use-After-Free Vulnerability
Mozilla - Firefox and Thunderbird · Listed in the CISA KEV since 2021-11-03. This indicates confirmed attacks in production environments.
Required action: Apply updates per vendor instructions.
CVE-2020-6820
HighCVSS 8.1KEVSummary
Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free. This vulnerability affects Thunderbird < 68.7.0, Firefox < 74.0.1, and Firefox ESR < 68.6.1. Targeted attacks in the wild abusing this flaw are known.
Risk Assessment
The vulnerability may allow arbitrary code execution or browser crashes, and due to active exploitation in the wild it poses a serious threat to organizations.
Recommendation
Update Thunderbird to version 68.7.0 or later, Firefox to 74.0.1 or later, and Firefox ESR to 68.6.1 or later.
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Multiple unspecified vulnerabilities in the browser engine in Mozilla Firefox before version 48.0 may allow remote attackers to cause a denial of service (memory corruption and application crash) or possibly execute arbitrary code via unknown vectors.
Original NVD description (English source)
Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Thunderbird < 68.7.0, Firefox < 74.0.1, and Firefox ESR < 68.6.1.