CVE-2026-110249: Denial-of-service in the Exchange email component

Published Oct 13, 2026
·
Updated

A malicious, compromised, or MITM-controlled Exchange server can return a single well-formed SOAP response containing an element with enough attributes to keep Thunderbird's main thread CPU-bound for seconds to hours.

Affected Software

3 affected componentsFixes available
Mozilla Thunderbird<158, <153.5
Mozilla Thunderbird<153.5
153.5
Mozilla Thunderbird<158
158

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 153.5
  2. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 158
  3. Upgrade

    Upgrade Thunderbird (use 158, or 153.5 on the 153 branch) to a version that resolves this vulnerability.

    Fixed in 158

Event History

Oct 13, 2026
CVE Published
via Mozilla·12:00 AM
Data Sourced
via Mozilla·12:00 AM
DescriptionSeverityAffected Software
CVE Published
via MITRE·06:08 PM
Data Sourced
via MITRE·06:08 PM
Description

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

Who is exposed to this denial-of-service issue?

Thunderbird users who connect the Exchange email component to a malicious or compromised Exchange server are exposed. Users whose Exchange traffic can be manipulated by a man-in-the-middle attacker are also exposed.

2

What does an attacker need to exploit the issue?

The attacker needs control of an Exchange server, compromise of a server the client uses, or the ability to act as a man in the middle for the Exchange connection. They can trigger the issue with a single well-formed SOAP response containing an element with a sufficiently large number of attributes.

3

What is the impact on an affected Thunderbird client?

Processing the crafted SOAP response can keep Thunderbird's main thread CPU-bound for seconds to hours. This results in a denial of service through loss of responsiveness.

4

Which Thunderbird releases contain the fix?

The issue was fixed in Thunderbird 158 and Thunderbird 153.5.

Company

Resources

Contact

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