# CVE-2026-113869: Thunderbird use-after-free in S/MIME decryption

Source: https://junglewise.ai/threats/cve-2026-113869-when-thunderbird-asked-for-a-security-device-password-for  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-20. Updated: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-113869 · Severity: medium · CVSS 5.4 · Published 2026-10-20

Thunderbird is an email client that handles encrypted messages using S/MIME. When Thunderbird prompts the user to enter a security device password (such as a smartcard PIN) to decrypt a message, an attacker could close or complete the message load while the prompt is open, causing the application to crash or potentially execute arbitrary code.

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

## Quick answers

**Is CVE-2026-113869 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-113869 being exploited in the wild.

**How severe is CVE-2026-113869?** Medium severity, with a CVSS score of 5.4, published 20 October 2026.

**Which products and versions are affected?** Mozilla Thunderbird before 158.0.1.

**Is there a fix for CVE-2026-113869?** Yes: fixed in Thunderbird 158.0.1. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-113869 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-113869?** 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 158.0.1

## Technical details

A use-after-free vulnerability in S/MIME message decryption occurs when the message decoder is freed while a security device password prompt is still active. If the message load completes or is cancelled during the prompt, the decoder is freed but subsequently referenced, leading to a crash. Exploitation requires the ability to send a specially crafted S/MIME message and user interaction to trigger the password prompt.

## Affected products

- Mozilla Thunderbird before 158.0.1

## Timeline

- 2026-10-20: disclosed

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2075530](https://bugzilla.mozilla.org/show_bug.cgi?id=2075530)
- [https://www.mozilla.org/security/advisories/mfsa2026-114/](https://www.mozilla.org/security/advisories/mfsa2026-114/)

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