# CVE-2026-74988: Mozilla Thunderbird memory corruption in ESR 153.0 and 153

Source: https://junglewise.ai/threats/cve-2026-74988-mozilla-thunderbird-memory-corruption-in-esr-153-0-and-153  
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-2026-74988 · Severity: critical · CVSS 9.8 · Published 2026-08-18

Thunderbird, a popular open-source email and calendar client used by millions worldwide, contained multiple internally-discovered security bugs that could lead to memory corruption. An attacker exploiting these flaws could potentially execute arbitrary code or crash the application, compromising user email data and system integrity. Mozilla fixed these issues in Thunderbird 154 and Thunderbird 153.1.

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

## Quick answers

**Is CVE-2026-74988 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-74988 being exploited in the wild.

**How severe is CVE-2026-74988?** Critical severity, with a CVSS score of 9.8, published 18 August 2026.

**Which products and versions are affected?** Mozilla Thunderbird 153.0; Mozilla Thunderbird ESR 153.0.

**Is there a fix for CVE-2026-74988?** A patch was published on 2026-08-18: Fixed in Thunderbird 154 and Thunderbird 153.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-74988 attacked?** It is attacked with local access.

**Am I affected by CVE-2026-74988?** Check whether you run Mozilla Thunderbird or Mozilla Thunderbird ESR 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

Multiple memory corruption and security-relevant defects were discovered through internal testing in Thunderbird ESR 153.0 and Thunderbird 153, affecting the core email and calendar client engine. The vulnerabilities stem from unspecified memory safety issues within the product, allowing potential code execution or denial of service depending on the specific flaw. No network access or user interaction is required if the attacker can reach the affected code paths. The vulnerabilities were patched in Thunderbird 154 and Thunderbird 153.1; users should upgrade immediately. There is no evidence of active exploitation in the wild at the time of disclosure.

## Affected products

- Mozilla Thunderbird 153.0
- Mozilla Thunderbird ESR 153.0

## Timeline

- 2026-08-18: disclosed: Publicly disclosed via NVD
- 2026-08-18: patched: Fixed in Thunderbird 154 and Thunderbird 153.1

## References

- [https://bugzilla.mozilla.org/buglist.cgi?bug_id=2018164%2C2045404%2C2045507%2C2045711%2C2052403%2C2053174%2C2054643%2C2054667%2C2054671%2C2054674%2C2054687%2C2054717%2C2054761%2C2054787%2C2055676%2C2056779%2C2056781%2C2058629%2C2059019%2C2059138](https://bugzilla.mozilla.org/buglist.cgi?bug_id=2018164%2C2045404%2C2045507%2C2045711%2C2052403%2C2053174%2C2054643%2C2054667%2C2054671%2C2054674%2C2054687%2C2054717%2C2054761%2C2054787%2C2055676%2C2056779%2C2056781%2C2058629%2C2059019%2C2059138)
- [https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045796%2C2046734%2C2051424%2C2054721%2C2057994%2C2058094%2C2058611%2C2058615%2C2058616%2C2061315](https://bugzilla.mozilla.org/buglist.cgi?bug_id=2045796%2C2046734%2C2051424%2C2054721%2C2057994%2C2058094%2C2058611%2C2058615%2C2058616%2C2061315)

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