NVD / CVE Program· CNA mozilla

CVE-2021-43528: Thunderbird unexpectedly enabled JavaScript in the composition area.

Noroxi assessment

Priority: Monitor (action score 26/100)

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: 1.3% (FIRST EPSS); higher than 70.6% of all records.
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 (AlmaLinux:8) 91.4.0-2.el8_5.alma, 91.4.0-2.el8_5.alma.plus; thunderbird (Debian:10) 1:91.4.1-1~deb10u1; thunderbird (Debian:11) 1:91.4.1-1~deb11u1.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to thunderbird (AlmaLinux:8) 91.4.0-2.el8_5.alma, 91.4.0-2.el8_5.alma.plus; thunderbird (Debian:10) 1:91.4.1-1~deb10u1; thunderbird (Debian:11) 1:91.4.1-1~deb11u1 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 unexpectedly enabled JavaScript in the composition area. The JavaScript execution context was limited to this area and did not receive chrome-level privileges, but could be used as a stepping stone to further an attack with other vulnerabilities. This vulnerability affects Thunderbird < 91.4.0.

MediumCVSS 6.5 · v3.1—No exploit Fix available

Pre-auth

Published: Dec 8, 2021
Updated: Jun 17, 2026
EPSS: 1.3% · 70th percentile
CWE: CWE-269

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 26 / 40 · 6.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 1.3%

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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?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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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
debian	debian linux	cpe:2.3:o:debian:debian_linux

Affected versions

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

debian debian linux10.0
debian debian linux11.0
debian debian linux9.0
mozilla thunderbirdbefore 91.4.0

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 91.4.0affected

Package-level exposure

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

Ecosystem	Package	Affected range	Fix
AlmaLinux:8	thunderbird	before 91.4.0-2.el8_5.alma	91.4.0-2.el8_5.alma
AlmaLinux:8	thunderbird	before 91.4.0-2.el8_5.alma.plus	91.4.0-2.el8_5.alma.plus
Debian:10	thunderbird	before 1:91.4.1-1~deb10u1	1:91.4.1-1~deb10u1
Debian:11	thunderbird	before 1:91.4.1-1~deb11u1	1:91.4.1-1~deb11u1
Debian:12	thunderbird	before 1:91.4.0-1	1:91.4.0-1
Debian:9	thunderbird	before 1:91.4.1-1~deb9u1	1:91.4.1-1~deb9u1
openSUSE:Tumbleweed	MozillaThunderbird	before 91.4.0-1.1	91.4.0-1.1
Red Hat:enterprise_linux:7::client	thunderbird	before 0:91.4.0-3.el7_9	0:91.4.0-3.el7_9
Red Hat:enterprise_linux:7::client	thunderbird-debuginfo	before 0:91.4.0-3.el7_9	0:91.4.0-3.el7_9
Red Hat:enterprise_linux:8::appstream	thunderbird	before 0:91.4.0-2.el8_5	0:91.4.0-2.el8_5
Red Hat:enterprise_linux:8::appstream	thunderbird-debuginfo	before 0:91.4.0-2.el8_5	0:91.4.0-2.el8_5
Red Hat:enterprise_linux:8::appstream	thunderbird-debugsource	before 0:91.4.0-2.el8_5	0:91.4.0-2.el8_5
Red Hat:rhel_e4s:8.1::appstream	thunderbird	before 0:91.4.0-2.el8_1	0:91.4.0-2.el8_1
Red Hat:rhel_e4s:8.1::appstream	thunderbird-debuginfo	before 0:91.4.0-2.el8_1	0:91.4.0-2.el8_1
Red Hat:rhel_e4s:8.1::appstream	thunderbird-debugsource	before 0:91.4.0-2.el8_1	0:91.4.0-2.el8_1
Red Hat:rhel_eus:8.2::appstream	thunderbird	before 0:91.4.0-2.el8_2	0:91.4.0-2.el8_2
Red Hat:rhel_eus:8.2::appstream	thunderbird-debuginfo	before 0:91.4.0-2.el8_2	0:91.4.0-2.el8_2
Red Hat:rhel_eus:8.2::appstream	thunderbird-debugsource	before 0:91.4.0-2.el8_2	0:91.4.0-2.el8_2
Red Hat:rhel_eus:8.4::appstream	thunderbird	before 0:91.4.0-2.el8_4	0:91.4.0-2.el8_4
Red Hat:rhel_eus:8.4::appstream	thunderbird-debuginfo	before 0:91.4.0-2.el8_4	0:91.4.0-2.el8_4
Red Hat:rhel_eus:8.4::appstream	thunderbird-debugsource	before 0:91.4.0-2.el8_4	0:91.4.0-2.el8_4
Rocky Linux:8	thunderbird	before 0:91.4.0-2.el8_5	0:91.4.0-2.el8_5

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-2021-29969Aug 5, 2021 · If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion
23Monitor
← EarlierCVE-2021-38502Nov 2, 2021 · Thunderbird ignored the configuration to require STARTTLS security for an SMTP connection.
23Monitor
Later →CVE-2020-15685Dec 22, 2022 · During the plaintext phase of the STARTTLS connection setup, protocol commands could have been injected and evaluated within the encrypted s
35Monitor

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
almalinux:thunderbird	91.4.0-2.el8_5.alma · AlmaLinux:8	Package registry (OSV)
debian:thunderbird	1:91.4.0-1 · Debian:12	Package registry (OSV)
opensuse:MozillaThunderbird	91.4.0-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
red hat:thunderbird	0:91.4.0-2.el8_5 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:thunderbird-debuginfo	0:91.4.0-2.el8_5 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
red hat:thunderbird-debugsource	0:91.4.0-2.el8_5 · Red Hat:enterprise_linux:8::appstream	Package registry (OSV)
rocky linux:thunderbird	0:91.4.0-2.el8_5 · Rocky Linux:8	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.

No history yet (it accumulates with the daily EPSS job).

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-21-0985 · Dec 10, 2021(RedHat Güvenlik Güncellemesi)

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: high · 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: High
Availability impact: None

Weakness class (CWE)

CWE-269 · Improper Privilege Management

CVSS vector

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

nvd-primary

Root cause

To simplify setup, a service account is granted broad, cluster-wide permissions. The principle of least privilege is skipped during installation.

The bug in code

The whole CWE-269 class

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

Vulnerable

yaml

1kind: ClusterRole
2rules:
3  - apiGroups: ["*"]
4    resources: ["*"]
5    verbs: ["*"]

Fixed

yaml

1kind: Role
2metadata:
3  namespace: lodos-system
4rules:
5  - apiGroups: ["apps"]
6    resources: ["deployments"]
7    verbs: ["get", "list", "update"]

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

Abuse Elevation Control MechanismT1548

Change log

Fix✗ → ✓Sep 28, 2026, 10:47 PM UTC

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

References

bugzilla.mozilla.org/show_bug.cgi?id=1742579

Show all references (4 more)

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

All records