Is CVE-2026-109777 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-109777 being exploited in the wild.

How severe is CVE-2026-109777?

Medium severity, with a CVSS score of 4.3, published 13 October 2026.

Which products and versions are affected?

Mozilla Firefox before 158; Mozilla Firefox ESR before 153.5; Mozilla Thunderbird before 153.5.

Is there a fix for CVE-2026-109777?

Yes: fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-109777 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-109777?

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.

CVE-2026-109777: Firefox Information disclosure in Storage: IndexedDB

CVE-2026-109777 · Severity: medium · CVSS 4.3 · Published 2026-10-13

Firefox and Thunderbird are web browsers and email clients that store user data including browsing history, passwords, and messages using IndexedDB. An attacker could exploit an information disclosure vulnerability in the IndexedDB storage component to access sensitive data stored by web applications. This vulnerability was fixed in recent versions of Firefox, Firefox ESR, and Thunderbird.

Technologies: Mozilla Firefox, Mozilla Firefox ESR, Mozilla Thunderbird. Vendors: Mozilla.

Quick answers

Is CVE-2026-109777 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-109777 being exploited in the wild.
How severe is CVE-2026-109777?: Medium severity, with a CVSS score of 4.3, published 13 October 2026.
Which products and versions are affected?: Mozilla Firefox before 158; Mozilla Firefox ESR before 153.5; Mozilla Thunderbird before 153.5.
Is there a fix for CVE-2026-109777?: Yes: fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-109777 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-109777?: 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.

How to fix

Fixed in: Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5

Technical details

An information disclosure vulnerability exists in the Storage: IndexedDB component that could expose user data or sensitive information to unauthorized access. The vulnerability affects Firefox, Firefox ESR, Thunderbird browsers and email clients, with fixes provided in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5. Network-based attack is likely given this is a storage component vulnerability.

Affected products

Mozilla Firefox before 158
Mozilla Firefox ESR before 153.5
Mozilla Thunderbird before 158
Mozilla Thunderbird before 153.5

Timeline

2026-10-13: advisory

References

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