Mozilla Firefox/Thunderbird MIME Type protection mechanism

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.
5.9$0-$5k0.00

Summaryinfo

A vulnerability categorized as critical has been discovered in Mozilla Firefox and Thunderbird. This issue affects some unknown processing of the component MIME Type Handler. Executing a manipulation can lead to protection mechanism. This vulnerability is handled as CVE-2020-26958. The attack can be executed remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Mozilla Firefox and Thunderbird (Web Browser) (affected version unknown). It has been declared as critical. This vulnerability affects an unknown functionality of the component MIME Type Handler. The manipulation with an unknown input leads to a protection mechanism vulnerability. The CWE definition for the vulnerability is CWE-693. The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product. As an impact it is known to affect confidentiality, integrity, and availability.

The weakness was released 12/09/2020 as mfsa2020-50. The advisory is shared for download at mozilla.org. This vulnerability was named CVE-2020-26958. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 02/09/2026).

Upgrading eliminates this vulnerability. The upgrade is hosted for download at mozilla.org.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-0337). Once again VulDB remains the best source for vulnerability data.

Affected

  • Open Source CentOS
  • Debian Linux
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • Gentoo Linux
  • Open Source Arch Linux
  • Mozilla Firefox
  • Mozilla Firefox ESR
  • Mozilla Thunderbird

Productinfo

Type

Vendor

Name

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.2
VulDB Meta Temp Score: 6.0

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

NVD Base Score: 6.1
NVD Vector: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

NVD Base Score: 🔍

Exploitinginfo

Class: Protection mechanism
CWE: CWE-693
CAPEC: 🔍
ATT&CK: 🔍

Physical: No
Local: No
Remote: Yes

Availability: 🔍
Status: Not defined

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔍

Upgrade: mozilla.org

Timelineinfo

10/12/2020 🔍
12/09/2020 +58 days 🔍
12/09/2020 +0 days 🔍
02/09/2026 +1888 days 🔍

Sourcesinfo

Vendor: mozilla.org
Product: mozilla.org

Advisory: mfsa2020-50
Status: Confirmed
Confirmation: 🔍

CVE: CVE-2020-26958 (🔍)
GCVE (CVE): GCVE-0-2020-26958
GCVE (VulDB): GCVE-100-165796
CERT Bund: WID-SEC-2026-0337 - Mozilla Firefox und Thunderbird: Mehrere Schwachstellen

Entryinfo

Created: 12/09/2020 10:48
Updated: 02/09/2026 10:28
Changes: 12/09/2020 10:48 (39), 12/14/2020 08:38 (6), 12/14/2020 08:44 (18), 02/09/2026 10:28 (21)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

Discussion

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