# CVE-2026-6748: Mozilla Firefox and Thunderbird uninitialized memory in Web Codecs

Source: https://junglewise.ai/threats/cve-2026-6748-mozilla-firefox-and-thunderbird-uninitialized-memory-in-web-codecs  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-21. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

CVE-2026-6748 · Severity: critical · CVSS 9.8 · Published 2026-04-21

A vulnerability exists in the web browsers and email clients Firefox and Thunderbird within the component responsible for processing audio and video content. This flaw could allow an attacker to potentially access sensitive information or execute unauthorized commands if a user visits a malicious website or interacts with malicious media content. While Thunderbird users are generally protected while reading standard emails, the risk remains in browser-like contexts within the application.

Technologies: [Mozilla Firefox](https://junglewise.ai/threats/technologies/firefox), [Mozilla Firefox ESR](https://junglewise.ai/threats/technologies/firefox-esr), [Mozilla Thunderbird](https://junglewise.ai/threats/technologies/thunderbird). Vendors: [Mozilla](https://junglewise.ai/threats/vendors/mozilla).

## Quick answers

**Is CVE-2026-6748 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-6748 being exploited in the wild.

**How severe is CVE-2026-6748?** Critical severity, with a CVSS score of 9.8, published 21 April 2026.

**Which products and versions are affected?** Mozilla Firefox < 150; Mozilla Firefox ESR < 140.10; Mozilla Thunderbird < 150, < 140.10.

**Is there a fix for CVE-2026-6748?** A patch was published on 2026-04-21. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-6748 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-6748?** Check whether you run Mozilla Firefox, Mozilla Firefox ESR or 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.

## Technical details

A vulnerability classified as 'Use of Uninitialized Variable' (CWE-457) or 'Access of Uninitialized Pointer' (CWE-824) exists in the Audio/Video: Web Codecs component of Mozilla browsers and email clients. The flaw occurs when the application attempts to use memory that has not been properly initialized, which can lead to memory corruption. An attacker can exploit this over the network by enticing a user to process specially crafted media content. Successful exploitation could result in information disclosure, a crash, or potentially arbitrary code execution. The issue is fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

## Affected products

- Mozilla Firefox < 150
- Mozilla Firefox ESR < 140.10
- Mozilla Thunderbird < 150, < 140.10
- Red Hat Enterprise Linux 7, 10.0

## Timeline

- 2026-04-21: disclosed
- 2026-04-21: patched
- 2026-04-21: advisory

## References

- [https://bugzilla.mozilla.org/show_bug.cgi?id=2022604](https://bugzilla.mozilla.org/show_bug.cgi?id=2022604)
- [https://www.mozilla.org/security/advisories/mfsa2026-30/](https://www.mozilla.org/security/advisories/mfsa2026-30/)
- [https://www.mozilla.org/security/advisories/mfsa2026-32/](https://www.mozilla.org/security/advisories/mfsa2026-32/)
- [https://www.mozilla.org/security/advisories/mfsa2026-33/](https://www.mozilla.org/security/advisories/mfsa2026-33/)
- [https://www.mozilla.org/security/advisories/mfsa2026-34/](https://www.mozilla.org/security/advisories/mfsa2026-34/)
- [https://access.redhat.com/errata/RHSA-2026:10757](https://access.redhat.com/errata/RHSA-2026:10757)
- [https://access.redhat.com/errata/RHSA-2026:10766](https://access.redhat.com/errata/RHSA-2026:10766)

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