# CVE-2026-110247: Integer overflow in libmime buffer growth could lead to heap corruption

> An integer overflow in libmime buffer growth allows heap corruption and potential code execution via crafted messages in Thunderbird.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/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:** Not needed
- **Fix available:** No
- **Published:** 13 Oct 2026
- **Updated:** 27 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-110247, GHSA-6c5g-4xv7-7fmm, UBUNTU-CVE-2026-110247

## What is CVE-2026-110247?

CVE-2026-110247 is a high-severity vulnerability in Mozilla Thunderbird, published on 13 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Several buffer-growth sites in libmime performed size arithmetic in 32-bit types without overflow checks. On a sufficiently large message the growth guard could fail open, or the buffer could be reallocated smaller than required, and a subsequent memcpy would then write attacker-controlled data across adjacent heap allocations. This vulnerability was fixed in Thunderbird 158 and Thunderbird 153.6.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-110247?


## How do I fix CVE-2026-110247?

No fix has been published for CVE-2026-110247 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-110247 being exploited?

There is no known exploitation of CVE-2026-110247 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-110247 and fix it if it is affected.

What it is: CVE-2026-110247 is a high-severity vulnerability in Mozilla Thunderbird, published on 13 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-110247 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-2026-110247/ (Markdown: https://insights.sbomify.com/CVE-2026-110247/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-110247
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-110247
- OSV: https://osv.dev/vulnerability/CVE-2026-110247

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-110247/
Summaries are generated and may contain mistakes; the official description above is the record.