# CVE-2026-74990: Mozilla Thunderbird memory corruption in internally found bugs

Source: https://junglewise.ai/threats/cve-2026-74990-mozilla-thunderbird-memory-corruption-in-internally-found-bugs  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-18. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-74990 · Severity: critical · CVSS 9.8 · Published 2026-08-18

Thunderbird is a widely-used open-source email and messaging client. Mozilla discovered multiple internal security flaws involving memory corruption and other defects that could potentially be exploited by attackers to crash the application, corrupt data, or execute arbitrary code. Updates are available to address these issues.

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

## Quick answers

**Is CVE-2026-74990 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-74990 being exploited in the wild.

**How severe is CVE-2026-74990?** Critical severity, with a CVSS score of 9.8, published 18 August 2026.

**Which products and versions are affected?** Mozilla Firefox ESR 115.x (before 115.39), ESR 140.13, ESR 153.0; Mozilla Thunderbird ESR 140.13, ESR 153.0, 153.

**Is there a fix for CVE-2026-74990?** A patch was published on 2026-08-18: Fixes available in Thunderbird 154, 153.1, ESR 140.14; Firefox 154, ESR 115.39, ESR 140.14, ESR 153.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-74990 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-74990?** Check whether you run Mozilla Firefox 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

This vulnerability encompasses multiple internally discovered bugs in Thunderbird and Firefox with evidence of memory corruption and security-relevant defects. The vulnerable components span various subsystems within the Thunderbird email client and Firefox browser engine. These bugs are exploitable remotely without authentication or user interaction under certain conditions. An attacker could leverage these vulnerabilities to achieve arbitrary code execution, memory disclosure, or denial of service. Patches are available in Thunderbird 154, Thunderbird 153.1, Thunderbird ESR 140.14, and corresponding Firefox releases.

## Affected products

- Mozilla Thunderbird ESR 140.13, ESR 153.0, 153
- Mozilla Firefox ESR 115.x (before 115.39), ESR 140.13, ESR 153.0

## Timeline

- 2026-08-18: disclosed: Vulnerability disclosed via NVD
- 2026-08-18: patched: Fixes available in Thunderbird 154, 153.1, ESR 140.14; Firefox 154, ESR 115.39, ESR 140.14, ESR 153.1

## References

- [https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045762%2C2052401%2C2058208](https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045762%2C2052401%2C2058208)
- [https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045774%2C2048490%2C2050864%2C2053159%2C2053260%2C2053261%2C2053582%2C2053599%2C2053607%2C2053608%2C2053853%2C2054626%2C2054627%2C2054635%2C2054677%2C2054740%2C2054832%2C2056792%2C2057098%2C2057100%2C2057101%2C2057103%2C2057117%2C2057118%2C2058048%2C2058049%2C2058622%2C2058623%2C2058665%2C2058666%2C2059121%2C2059164%2C2059188](https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045774%2C2048490%2C2050864%2C2053159%2C2053260%2C2053261%2C2053582%2C2053599%2C2053607%2C2053608%2C2053853%2C2054626%2C2054627%2C2054635%2C2054677%2C2054740%2C2054832%2C2056792%2C2057098%2C2057100%2C2057101%2C2057103%2C2057117%2C2057118%2C2058048%2C2058049%2C2058622%2C2058623%2C2058665%2C2058666%2C2059121%2C2059164%2C2059188)

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