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CVE-2020-6820

59
FAUCET Score

CVE-2020-6820 is a high-severity use-after-free vulnerability affecting Mozilla Firefox, Firefox ESR, and Thunderbird versions prior to 74.0.1, 68.6.1, and 68.7.0 respectively. This flaw arises from a race condition during ReadableStream handling, which can lead to remote code execution. With a CVSS score of 8.1 (HIGH), it presents a significant risk due to its network-based attack vector, high impact on confidentiality, integrity, and availability, and low attack complexity. The vulnerability is actively exploited in the wild, as confirmed by its presence in the CISA KEV catalog. While no public exploit code is available via Metasploit, Nuclei, or ExploitDB, its active exploitation underscores the urgency of patching. Despite limited community discussion, the vulnerability has received significant media coverage, indicating its critical nature and the awareness of its active exploitation.

Impacted Technologies

VendorProductVersion(s)CPE
< 68.6.1CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
< 74.0.1CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
< 68.7.0CPE matchmatch criteria
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.1HIGH

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.2
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
6.30%
Probability of exploitation in next 30 days
EPSS Percentile
92.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Added to KEV · Nov 3, 2021
This CVE's current EPSS score of 0.0630 is in the 67th percentile among its peer group of 8,920 CVEs.

Social Chatter

No social media mentions found for this CVE.

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (9)

redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.0 Update Services for SAP SolutionsFixed in: thunderbird-0:68.7.0-1.el8_0
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: firefox-0:68.6.1-1.el6_10
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: thunderbird-0:68.7.0-1.el6_10
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: firefox-0:68.6.1-1.el7_8
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: thunderbird-0:68.7.0-1.el7_8
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: firefox-0:68.6.1-1.el8_1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: thunderbird-0:68.7.0-1.el8_1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.0 Update Services for SAP SolutionsFixed in: firefox-0:68.6.1-1.el8_0
View patch
mozillavendor investigatingvia nvd_reference
View patch

Vendor Advisories (1)

redhatCVE-2020-6820Critical

Mozilla: Use-after-free when handling a ReadableStream

Apr 3, 2020

References

cisa.gov / known-exploited-vulnerabilities-catalog
US Government Resource
bugzilla.mozilla.org / show_bug.cgi
Issue TrackingPermissions Required
usn.ubuntu.com / 4335-1
Third Party Advisory
mozilla.org / security/advisories/mfsa2020-11
Vendor Advisory
mozilla.org / security/advisories/mfsa2020-14
Vendor Advisory