Early Access — Mondoo Vulnerability Intelligence is currently in preview.

CVE-2020-6820

HIGH8.1

Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free

Published Apr 24, 2020

Modified 2 months ago

Fix available

Details

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.

Affected Packages

Ubuntu:14.04:LTSFirefox

Fixed in:

74.0.1

Ubuntu:16.04:LTSFirefox

Fixed in:

74.0.1

Ubuntu:18.04:LTSFirefox

Fixed in:

74.0.1

Ubuntu:20.04:LTSFirefox

Fixed in:

74.0.1

Ubuntu:22.04:LTSFirefox

Fixed in:

74.0.1

Ubuntu:24.04:LTSFirefox

Fixed in:

74.0.1

Ubuntu:25.04Firefox

Fixed in:

74.0.1

Ubuntu:25.10Firefox

Fixed in:

74.0.1

Windows:10240Mozilla Firefox

Fixed in:

74.0.1

Windows:10240Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:14393Mozilla Firefox

Fixed in:

74.0.1

Windows:14393Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:17763Mozilla Firefox

Fixed in:

74.0.1

Windows:17763Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:18362Mozilla Firefox

Fixed in:

74.0.1

Windows:18362Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:18363Mozilla Firefox

Fixed in:

74.0.1

Windows:18363Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:19041Mozilla Firefox

Fixed in:

74.0.1

Windows:19041Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:19042Mozilla Firefox

Fixed in:

74.0.1

Windows:19042Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:19043Mozilla Firefox

Fixed in:

74.0.1

Windows:19043Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:19044Mozilla Firefox

Fixed in:

74.0.1

Windows:19044Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:19045Mozilla Firefox

Fixed in:

74.0.1

Windows:19045Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:20348Mozilla Firefox

Fixed in:

74.0.1

Windows:20348Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:22000Mozilla Firefox

Fixed in:

74.0.1

Windows:22000Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:22621Mozilla Firefox

Fixed in:

74.0.1

Windows:22621Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:22631Mozilla Firefox

Fixed in:

74.0.1

Windows:22631Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:25398Mozilla Firefox

Fixed in:

74.0.1

Windows:25398Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:26100Mozilla Firefox

Fixed in:

74.0.1

Windows:26100Mozilla Firefox ESR

Fixed in:

68.6.1

Windows:26200Mozilla Firefox

Fixed in:

74.0.1

Windows:26200Mozilla Firefox ESR

Fixed in:

68.6.1

macOS:14Firefox

Fixed in:

74.0.1

macOS:14Firefox ESR

Fixed in:

68.6.1

macOS:15Firefox

Fixed in:

74.0.1

macOS:15Firefox ESR

Fixed in:

68.6.1

macOS:26Firefox

Fixed in:

74.0.1

macOS:26Firefox ESR

Fixed in:

68.6.1

References

WEBhttps://bugzilla.mozilla.org/show_bug.cgi?id=1626728 ADVISORYhttps://usn.ubuntu.com/4335-1/WEBhttps://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6820 ADVISORYhttps://www.cve.org/CVERecord?id=CVE-2020-6820 WEBhttps://www.mozilla.org/security/advisories/mfsa2020-11/WEBhttps://www.mozilla.org/security/advisories/mfsa2020-14/

CVSS Analysis

CVSS v3.1

8.1

Exploitability

Attack Vector

NetworkAV:N

Attack Complexity

HighAC:H

Privileges Required

NonePR:N

User Interaction

NoneUI:N

Scope

Scope

UnchangedS:U

Impact

Confidentiality

HighC:H

Integrity

HighI:H

Availability

HighA:H

8.1/CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Timeline

PublishedApr 24, 2020

ModifiedOct 21, 2025

CVE-2020-6820 | Mondoo Vulnerability Intelligence