Exploited vulnerability · CISA KEV

Is CVE-2020-6820 exploited? Yes: in CISA KEV since 3 Nov 2021

Gociux · Mozilla Firefox and Thunderbird · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2020-6820, Mozilla Firefox And Thunderbird Use-After-Free Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 558 days after it was published. It affects Mozilla Firefox and Thunderbird. If you run it, CISA's required action is: Apply updates per vendor instructions.

exploitedYesCISA KEV · 3 Nov 2021

ransomwareNot knownno confirmed use

EPSStop 10%more likely than most to be exploited

severity8.1CVSS 3.1 · high

US federal due3 May 2022BOD 22-01 deadline

What it is

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.

Vendor	Mozilla (13 exploited CVEs in KEV)
Product	Firefox and Thunderbird
Vulnerability	Mozilla Firefox And Thunderbird Use-After-Free Vulnerability
Weakness	CWE-362
Published	24 Apr 2020
Added to KEV	3 Nov 2021
Reported by (CNA)	mozilla

What to do

Check whether you run it. Look for Firefox and Thunderbird in your asset inventory, including appliances and cloud images. Stack check lists every exploited Mozilla CVE at once.
Apply the fix. Apply updates per vendor instructions.
If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 24 Apr 2020.
Get told next time. Email alerts when CISA adds a CVE for Mozilla.

Other exploited CVEs in Firefox and Thunderbird

CVE-2019-11707: Mozilla Firefox and Thunderbird Type Confusion Vulnerability (23 May 2022)
CVE-2019-11708: Mozilla Firefox and Thunderbird Sandbox Escape Vulnerability (23 May 2022)
CVE-2013-1690: Mozilla Firefox and Thunderbird Denial-of-Service Vulnerability (28 Mar 2022)
CVE-2020-6819: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability (3 Nov 2021)
CVE-2019-17026: Mozilla Firefox And Thunderbird Type Confusion Vulnerability (3 Nov 2021)

References

nvd.nist.gov/vuln/detail/CVE-2020-6820

Questions

Is CVE-2020-6820 being exploited?

Yes. CISA added CVE-2020-6820 to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, which means there is reliable evidence of exploitation in the wild.

Is CVE-2020-6820 used in ransomware attacks?

CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.

How do I fix CVE-2020-6820?

Apply updates per vendor instructions. Check Mozilla's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected Firefox and Thunderbird and watch it for signs of compromise.

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Mozilla scorecard · act-now radar.

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