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CVE-2019-9821

20
FAUCET Score

CVE-2019-9821 describes a use-after-free vulnerability in Mozilla Firefox versions prior to 67, stemming from a race condition within the AssertWorkerThread function when handling shared workers. This flaw carries a high severity CVSS score of 8.1, indicating a potentially exploitable crash that could lead to high impact on confidentiality, integrity, and availability, with a network attack vector and high attack complexity. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
< 67.0CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
< 67CPE match
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

8.1HIGH

CVSS:3.0/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
3.0

Exploit Intelligence

EPSS Score
0.85%
Probability of exploitation in next 30 days
EPSS Percentile
54.4%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0085 is in the 22nd 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

No media coverage found for this CVE.

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

Remediation

Vendor Patches (1)

mozillavendor investigatingvia nvd_reference
View patch

Vendor Advisories (1)

redhatCVE-2019-9821Low

firefox: use-after-free in AssertWorkerThread leading to crash

May 21, 2019

References

bugzilla.mozilla.org / show_bug.cgi
Permissions RequiredVendor Advisory
mozilla.org / security/advisories/mfsa2019-13
Vendor Advisory