What is CVE-2020-15670?

CVE-2020-15670 is a high-severity vulnerability in Mozilla Firefox, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 8.8/10. Published 2020-10-01.

How severe is CVE-2020-15670?

High severity. CVSS v3 base score is 8.8 out of 10.

Is CVE-2020-15670 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Use After Free in Mozilla Firefox

CVE-2020-15670

Mozilla developers reported memory safety bugs present in Firefox for Android 79. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 80, Firefox ESR < 78.2, Thunderbird < 78.2, and Firefox for Android < 80.

Vulnerability class: Race Condition

Published 2020-10-01 · last modified 2026-08-19.

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.011 (63.5th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 63rd percentile — 63.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.011 · newest: 0.011 · change: +0.000

Affected products

Mozilla Firefox — versions unspecified
Mozilla Firefox Esr — versions unspecified
Mozilla Firefox Esr
Mozilla Firefox For Android — versions unspecified
Mozilla Firefox Mobile
Mozilla Thunderbird — versions unspecified

Weakness classification (CWE)

Public proof-of-concept exploits

Cheroxx/Patch-Tuesday-Updates

References

www.mozilla.org/security/advisories/mfsa2020-39/ (Release Notes, Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2020-41/ (Release Notes, Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2020-36/ (Release Notes, Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2020-38/ (Release Notes, Vendor Advisory)
bugzilla.mozilla.org/buglist.cgi (Issue Tracking, Broken Link, Vendor Advisory)

Frequently asked questions

What is CVE-2020-15670?: CVE-2020-15670 is a high-severity vulnerability in Mozilla Firefox, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 8.8/10. Published 2020-10-01.
How severe is CVE-2020-15670?: High severity. CVSS v3 base score is 8.8 out of 10.
Is CVE-2020-15670 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.