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CVE-2020-6820 High

Confirmed as exploited

CVE-2020-6820

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.

Exploit probability 6.3%
Published April 24, 2020
Required by May 3, 2022
Last source change April 16, 2026

01 / ACTION

Required action

Apply updates per vendor instructions.

02 / AFFECTED SOFTWARE

Affected packages

Unknown Unknown

03 / CONNECTIONS

Connected vulnerabilities

04 / EVIDENCE

Source records

Cybersecurity and Infrastructure Security Agency Known Exploited Vulnerabilities CVE-2020-6820

Mozilla Firefox and Thunderbird contain a race condition vulnerability when handling a ReadableStream under certain conditions. The race condition creates a use-after-free vulnerability, causing unspecified impacts.

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Open Source Vulnerabilities CVE-2020-6820

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.

View original source

05 / REFERENCES

Further evidence