# CVE-2026-110249: Thunderbird denial-of-service in Exchange component

Source: https://junglewise.ai/threats/cve-2026-110249-a-malicious-compromised-or-mitm-controlled-exchange-server-can  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-13. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-110249 · Severity: info · Published 2026-10-13

A malicious or compromised Exchange email server can send a specially crafted response that causes Thunderbird to become unresponsive for seconds to hours. This could be exploited by attackers controlling the email server or intercepting network traffic between a user and their mail server, disrupting email access.

Technologies: [Mozilla Thunderbird](https://junglewise.ai/threats/technologies/thunderbird). Vendors: [Mozilla](https://junglewise.ai/threats/vendors/mozilla).

## Quick answers

**Is CVE-2026-110249 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-110249 being exploited in the wild.

**How severe is CVE-2026-110249?** Informational severity, published 13 October 2026.

**Which products and versions are affected?** Mozilla Thunderbird before 158, before 153.5.

**Is there a fix for CVE-2026-110249?** Yes: fixed in Thunderbird 158, Thunderbird 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-110249 attacked?** It is attacked over the network or from the adjacent network, in a software library.

**Am I affected by CVE-2026-110249?** Check whether you run Mozilla Thunderbird at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in Thunderbird 158, Thunderbird 153.5

## Technical details

A SOAP response element with excessive attributes causes CPU-bound processing on Thunderbird's main thread, creating a denial-of-service condition. The vulnerability requires the attacker to control or intercept the Exchange server connection. The flaw was resolved in Thunderbird 158 and 153.5.

## Affected products

- Mozilla Thunderbird before 158, before 153.5

## Timeline

- 2026-10-13: disclosed

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2077826](https://bugzilla.mozilla.org/show_bug.cgi?id=2077826)
- [https://www.mozilla.org/security/advisories/mfsa2026-109/](https://www.mozilla.org/security/advisories/mfsa2026-109/)

## Related threats

- [Thunderbird OAuth2 access token leak over HTTP with Exchange accounts](https://junglewise.ai/threats/cve-2026-126136-for-exchange-accounts-using-ews-or-microsoft-graph-with-oauth2)
- [Mozilla Thunderbird SMTP/POP3 response injection via STARTTLS](https://junglewise.ai/threats/cve-2026-126135-if-an-attacker-was-able-to-perform-a-man-in-the-middle-attack-on)
- [Thunderbird NTLM credential leak via feed subscription to file URL](https://junglewise.ai/threats/cve-2026-126134-thunderbird-allowed-feed-subscriptions-to-file-urls-that-point)
- [Thunderbird calendar server credentials sent to HTTP proxy](https://junglewise.ai/threats/cve-2026-126133-when-a-caldav-or-ics-calendar-was-accessed-through-an-http-proxy)
- [Thunderbird attachment replacement disclosure via link files](https://junglewise.ai/threats/cve-2026-126132-when-a-message-was-forwarded-inline-edited-as-new-or-had-an)