VDB-358443 · CVE-2026-6746 · Nessus 309101

Mozilla Firefox up to 149 HTML use after free

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
6.7	$5k-$25k	0.00

Summaryinfo

A vulnerability, which was classified as critical, has been found in Mozilla Firefox up to 149. This affects an unknown function of the component HTML Component. Performing a manipulation results in use after free. This vulnerability was named CVE-2026-6746. The attack may be initiated remotely. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Mozilla Firefox up to 149. This affects an unknown functionality of the component HTML Component. The manipulation with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

It is possible to read the advisory at bugzilla.mozilla.org. This vulnerability is uniquely identified as CVE-2026-6746 since 04/21/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 07/02/2026).

The vulnerability scanner Nessus provides a plugin with the ID 309101 (Mozilla Thunderbird < 140.10), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 150 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (309101) and CERT Bund (WID-SEC-2026-1228). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

Debian Linux
Red Hat Enterprise Linux
SUSE Linux
Oracle Linux
SUSE openSUSE
RESF Rocky Linux
Mozilla Thunderbird
Mozilla Firefox ESR
Mozilla Firefox

Productinfo

Type

Web Browser

Vendor

Mozilla

Name

Firefox

Version

License

open-source

Website

Vendor: https://www.mozilla.org/
Product: https://www.mozilla.org/en-US/firefox/

CPE 2.3info

🔒

CPE 2.2info

🔒

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.9
VulDB Meta Temp Score: 6.7

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

ADP CISA Base Score: 7.5
ADP CISA Vector: 🔒

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 309101
Nessus Name: Mozilla Thunderbird < 140.10

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Firefox 150

Timelineinfo

04/21/2026 Advisory disclosed
04/21/2026 +0 days CVE reserved
04/21/2026 +0 days VulDB entry created
07/02/2026 +72 days VulDB entry last update

Sourcesinfo

Vendor: mozilla.org
Product: mozilla.org

Advisory: bugzilla.mozilla.org
Status: Confirmed

CVE: CVE-2026-6746 (🔒)
GCVE (CVE): GCVE-0-2026-6746
GCVE (VulDB): GCVE-100-358443
CERT Bund: WID-SEC-2026-1228 - Mozilla Thunderbird, Firefox ESR und Firefox: Mehrere Schwachstellen

Entryinfo

Created: 04/21/2026 15:54
Updated: 07/02/2026 08:42
Changes: 04/21/2026 15:54 (56), 04/22/2026 16:20 (2), 05/15/2026 11:19 (7), 07/02/2026 08:42 (12)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.