Mozilla Thunderbird up to 140.12/152 MIME Header Parsing off-by-one

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.
7.0$5k-$25k2.82

Summaryinfo

A vulnerability labeled as critical has been found in Mozilla Thunderbird up to 140.12/152. Affected by this vulnerability is an unknown functionality of the component MIME Header Parsing. Such manipulation leads to off-by-one. This vulnerability is listed as CVE-2026-14899. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Mozilla Thunderbird up to 140.12/152. Affected by this issue is an unknown part of the component MIME Header Parsing. The manipulation with an unknown input leads to a off-by-one vulnerability. Using CWE to declare the problem leads to CWE-193. A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value. Impacted is confidentiality, integrity, and availability. CVE summarizes:

The code to parse MIME headers for display when forwarding a message (if the setting to view all headers was enabled) had an off-by-one error, allowing a single byte to be read from the memory after the buffer for the headers, and potentially crashing Thunderbird. This vulnerability was fixed in Thunderbird 153 and Thunderbird 140.13.

The advisory is shared for download at bugzilla.mozilla.org. This vulnerability is handled as CVE-2026-14899 since 07/06/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $5k-$25k (estimation calculated on 07/23/2026).

The vulnerability scanner Nessus provides a plugin with the ID 329091 (Mozilla Thunderbird < 140.13), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 140.13 or 153 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (329091). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.3
VulDB Meta Temp Score: 7.0

VulDB Base Score: 7.3
VulDB Temp Score: 7.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
💳💳💳💳💳💳
💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
UnlockUnlockUnlockUnlockUnlockUnlock
UnlockUnlockUnlockUnlockUnlockUnlock
UnlockUnlockUnlockUnlockUnlockUnlock

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

Exploitinginfo

Class: Off-by-one
CWE: CWE-193 / CWE-189
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-DayUnlockUnlockUnlockUnlock
TodayUnlockUnlockUnlockUnlock

Nessus ID: 329091
Nessus Name: Mozilla Thunderbird < 140.13

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Thunderbird 140.13/153

Timelineinfo

07/06/2026 CVE reserved
07/22/2026 +16 days Advisory disclosed
07/22/2026 +0 days VulDB entry created
07/23/2026 +1 days VulDB entry last update

Sourcesinfo

Vendor: mozilla.org

Advisory: bugzilla.mozilla.org
Status: Confirmed

CVE: CVE-2026-14899 (🔒)
GCVE (CVE): GCVE-0-2026-14899
GCVE (VulDB): GCVE-100-382448

Entryinfo

Created: 07/22/2026 23:30
Updated: 07/23/2026 10:39
Changes: 07/22/2026 23:30 (55), 07/23/2026 10:39 (2)
Complete: 🔍
Cache ID: 216::103

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Discussion

No comments yet. Languages: en.

Please log in to comment.

◂ PreviousOverviewNext ▸

Want to know what is going to be exploited?

We predict KEV entries!