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

> A malicious Exchange server can cause Thunderbird to hang for extended periods by sending a crafted SOAP response, requiring an upgrade to fix.

- **Severity:** High 8.6 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 13 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-110249, GHSA-3vgg-r2jh-qqpj, UBUNTU-CVE-2026-110249

## What is CVE-2026-110249?

CVE-2026-110249 is a high-severity denial of service vulnerability in Mozilla Thunderbird, published on 13 Oct 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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. This vulnerability was fixed in Thunderbird 158 and Thunderbird 153.5.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-110249?


## How do I fix CVE-2026-110249?

Upgrade to a fixed version.

## Is CVE-2026-110249 being exploited?

There is no known exploitation of CVE-2026-110249 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-110249 and fix it if it is affected.

What it is: CVE-2026-110249 is a high-severity denial of service vulnerability in Mozilla Thunderbird, published on 13 Oct 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-110249 in the wild and no public exploit code.

Affected product: Mozilla Thunderbird. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-110249/ (Markdown: https://insights.sbomify.com/CVE-2026-110249/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-110249
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-110249
- OSV: https://osv.dev/vulnerability/CVE-2026-110249

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-110249/
Summaries are generated and may contain mistakes; the official description above is the record.