Is CVE-2021-23993 in the CISA KEV catalog?

No. CVE-2021-23993 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-23993?

CVE-2021-23993 has a CVSS v3 base score of 6.5 (MEDIUM).

What is the EPSS score for CVE-2021-23993?

CVE-2021-23993 has an EPSS score of 0.43% (34th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-23993?

Upgrade thunderbird on debian 11 to 1:78.10.0-1 or later. Fixes are available for 3 affected products.

CVE & CISA-KEV Catalog

CVE-2021-23993

MEDIUM

6.5

CVSS v3

NVD

Description

An attacker may perform a DoS attack to prevent a user from sending encrypted email to a correspondent. If an attacker creates a crafted OpenPGP key with a subkey that has an invalid self signature, and the Thunderbird user imports the crafted key, then Thunderbird may try to use the invalid subkey, but the RNP library rejects it from being used, causing encryption to fail. This vulnerability affects Thunderbird < 78.9.1.

CWE-347

How to fix

Remediation Available

thunderbirdDebian

Fixed in:1:78.10.0-1CVE-2021-23993

thunderbirdUbuntu

Fixed in:1:78.11.0+build1-0ubuntu0.18.04.2USN-4995-2

Fixed in:1:78.11.0+build1-0ubuntu0.20.04.2USN-4995-1

Mozilla Thunderbird (en-US)Windows application

Affected:78.9.1Fixed in:78.9.1Mozilla

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

0.43%probability of exploitation in 30 days

34thpercentile

Low risk: more likely to be exploited than 34% of all known CVEs.

References

Vendor Advisory2

Related Vulnerabilities

Other CWE-347 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2018-16042	Medium	6.5	82%	-	-
CVE-2025-59718	Critical	9.8	66%	KEV	Fix
CVE-2025-25292	Critical	9.8	64%	-	Fix
CVE-2021-22160	Critical	9.8	53%	-	Fix
CVE-2013-3900	Medium	5.5	45%	KEV	-
CVE-2018-0114	High	7.5	43%	-	Fix

Embed a live status badge for CVE-2021-23993

Markdown

[![CVE-2021-23993](https://tridentstack.com/cve/badge/CVE-2021-23993.svg)](https://tridentstack.com/cve/CVE-2021-23993)

HTML

<a href="https://tridentstack.com/cve/CVE-2021-23993"><img src="https://tridentstack.com/cve/badge/CVE-2021-23993.svg" alt="CVE-2021-23993"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.