NVD / CVE Program· CNA mozilla

CVE-2021-23992: Thunderbird did not check if the user ID associated with an OpenPGP key has a valid self signature.

Noroxi assessment

Priority: Monitor (action score 17/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.47% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
Fixed version: thunderbird (Debian:10) 1:78.10.0-1~deb10u1; thunderbird (Debian:12) 1:78.10.0-1; thunderbird (Debian:9) 1:78.10.0-1~deb9u1.
Mentioned 3 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to thunderbird (Debian:10) 1:78.10.0-1~deb10u1; thunderbird (Debian:12) 1:78.10.0-1; thunderbird (Debian:9) 1:78.10.0-1~deb9u1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Thunderbird did not check if the user ID associated with an OpenPGP key has a valid self signature. An attacker may create a crafted version of an OpenPGP key, by either replacing the original user ID, or by adding another user ID. If Thunderbird imports and accepts the crafted key, the Thunderbird user may falsely conclude that the false user ID belongs to the correspondent. This vulnerability affects Thunderbird < 78.9.1.

MediumCVSS 4.3 · v3.1—No exploit Fix available

Published: Jun 24, 2021
Updated: Jun 16, 2026
EPSS: 0.4% · 40th percentile
CWE: CWE-347

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 17 / 40 · 4.3 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

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Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
mozilla	thunderbird	cpe:2.3:a:mozilla:thunderbird

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

mozilla thunderbirdbefore 78.9.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (mozilla). Independent of NVD's CPE analysis and usually ahead of it.

Mozilla Thunderbird
- unspecified and later · before 78.9.1affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:10	thunderbird	before 1:78.10.0-1~deb10u1	1:78.10.0-1~deb10u1
Debian:12	thunderbird	before 1:78.10.0-1	1:78.10.0-1
Debian:9	thunderbird	before 1:78.10.0-1~deb9u1	1:78.10.0-1~deb9u1
openSUSE:Leap 15.2	MozillaThunderbird	before 78.9.1-lp152.2.38.1	78.9.1-lp152.2.38.1
Red Hat:enterprise_linux:7::client	thunderbird	before 0:78.9.1-1.el7_9	0:78.9.1-1.el7_9
Red Hat:enterprise_linux:7::client	thunderbird-debuginfo	before 0:78.9.1-1.el7_9	0:78.9.1-1.el7_9
Red Hat:enterprise_linux:8::appstream	thunderbird	before 0:78.9.1-1.el8_3	0:78.9.1-1.el8_3
Red Hat:enterprise_linux:8::appstream	thunderbird-debuginfo	before 0:78.9.1-1.el8_3	0:78.9.1-1.el8_3
Red Hat:enterprise_linux:8::appstream	thunderbird-debugsource	before 0:78.9.1-1.el8_3	0:78.9.1-1.el8_3
Red Hat:rhel_eus:8.1::appstream	thunderbird	before 0:78.9.1-1.el8_1	0:78.9.1-1.el8_1
Red Hat:rhel_eus:8.1::appstream	thunderbird-debuginfo	before 0:78.9.1-1.el8_1	0:78.9.1-1.el8_1
Red Hat:rhel_eus:8.1::appstream	thunderbird-debugsource	before 0:78.9.1-1.el8_1	0:78.9.1-1.el8_1
Red Hat:rhel_eus:8.2::appstream	thunderbird	before 0:78.9.1-1.el8_2	0:78.9.1-1.el8_2
Red Hat:rhel_eus:8.2::appstream	thunderbird-debuginfo	before 0:78.9.1-1.el8_2	0:78.9.1-1.el8_2
Red Hat:rhel_eus:8.2::appstream	thunderbird-debugsource	before 0:78.9.1-1.el8_2	0:78.9.1-1.el8_2
SUSE:Linux Enterprise Workstation Extension 15 SP2	MozillaThunderbird	before 78.9.1-8.20.1	78.9.1-8.20.1

Same product

mozilla: all records

Other highest-scoring records for the same primary product.

CVE-2019-11705A flaw in Thunderbird's implementation of iCal causes a stack buffer overflow in icalrecur_add_bydayrules when processing certain email mess
42Plan
CVE-2019-11704A flaw in Thunderbird's implementation of iCal causes a heap buffer overflow in icalmemory_strdup_and_dequote when processing certain email
42Plan
CVE-2019-11703A flaw in Thunderbird's implementation of iCal causes a heap buffer overflow in parser_get_next_char when processing certain email messages,
42Plan

Published before and after this one in the same product

← EarlierCVE-2020-26970Dec 8, 2020 · When reading SMTP server status codes, Thunderbird writes an integer value to a position on the stack that is intended to contain just one b
35Monitor
← EarlierCVE-2021-23991Jun 24, 2021 · If a Thunderbird user has previously imported Alice's OpenPGP key, and Alice has extended the validity period of her key, but Alice's update
27Monitor
Later →CVE-2021-23993Jun 24, 2021 · An attacker may perform a DoS attack to prevent a user from sending encrypted email to a correspondent.
26Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
debian:thunderbird	1:78.10.0-1 · Debian:12	Package registry (OSV)
opensuse:MozillaThunderbird	78.9.1-lp152.2.38.1 · openSUSE:Leap 15.2	Package registry (OSV)
red hat:thunderbird	0:78.9.1-1.el8_1 · Red Hat:rhel_eus:8.1::appstream	Package registry (OSV)
red hat:thunderbird-debuginfo	0:78.9.1-1.el8_1 · Red Hat:rhel_eus:8.1::appstream	Package registry (OSV)
red hat:thunderbird-debugsource	0:78.9.1-1.el8_1 · Red Hat:rhel_eus:8.1::appstream	Package registry (OSV)
suse:MozillaThunderbird	78.9.1-8.20.1 · SUSE:Linux Enterprise Workstation Extension 15 SP2	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-21-0523 · Jun 28, 2021(Ubuntu Güvenlik Bildirimi Yayınladı)
TR-21-0329 · Apr 19, 2021(CentOS 7 Güncellemesi)
TR-21-0323 · Apr 16, 2021(RedHat Güvenlik Güncellemeleri Yayınladı)

All national notices →

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
A user must open a link or visit a page.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: low · data or configuration can be modified
Availability: none

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Unchanged
Confidentiality impact: None
Integrity impact: Low
Availability impact: None

Weakness class (CWE)

CWE-347 · Improper Verification of Cryptographic Signature

CVSS vector

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

nvd-primary

Root cause

The verifier takes the algorithm to verify with from the token’s own header. Untrusted data ends up deciding its own verification rule.

The bug in code

The whole CWE-347 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const claims = jwt.verify(token, publicKey);

Fixed

1const claims = jwt.verify(token, publicKey, {
2  algorithms: ["RS256"],
3  issuer: "https://id.example.com",
4  audience: "portal",
5});

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:45 PM UTC

For records you follow, these changes also arrive as notifications. →

References

bugzilla.mozilla.org/show_bug.cgi?id=1666236

Show all references (1 more)

www.mozilla.org/security/advisories/mfsa2021-13/

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records