Is CVE-2026-5735 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-5735 being exploited in the wild.

How severe is CVE-2026-5735?

Critical severity, with a CVSS score of 9.8, published 7 April 2026.

Which products and versions are affected?

Mozilla Firefox < 149.0.2; Mozilla Thunderbird < 149.0.2.

Is there a fix for CVE-2026-5735?

A patch was published on 2026-04-07. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-5735 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-5735?

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.

CVE-2026-5735: Mozilla Firefox and Thunderbird memory safety bugs

Q: Which products and versions are affected?

Mozilla Firefox < 149.0.2; Mozilla Thunderbird < 149.0.2.

Q: Is there a fix for CVE-2026-5735?

A patch was published on 2026-04-07. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-5735 attacked?

It is attacked over the network, in a network appliance.

Q: Am I affected by CVE-2026-5735?

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.

CVE-2026-5735 · Severity: critical · CVSS 9.8 · Published 2026-04-07

Mozilla Firefox and Thunderbird are popular web browser and email applications. Multiple memory safety vulnerabilities have been identified that could allow an attacker to crash the application or potentially execute unauthorized code on a user's computer. This could lead to the theft of sensitive data, unauthorized access to accounts, or full system compromise if a user visits a malicious website or interacts with malicious content.

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

Quick answers

Is CVE-2026-5735 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-5735 being exploited in the wild.
How severe is CVE-2026-5735?: Critical severity, with a CVSS score of 9.8, published 7 April 2026.
Which products and versions are affected?: Mozilla Firefox < 149.0.2; Mozilla Thunderbird < 149.0.2.
Is there a fix for CVE-2026-5735?: A patch was published on 2026-04-07. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-5735 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-5735?: 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

Mozilla developers and the fuzzing team identified several memory safety bugs in Firefox and Thunderbird. These vulnerabilities include out-of-bounds writes (CWE-787) and out-of-bounds reads (CWE-125) that exhibit evidence of memory corruption. An attacker could potentially exploit these flaws via a network-based attack vector to achieve arbitrary code execution. While Thunderbird's default configuration disables scripting in emails, reducing the risk, the vulnerabilities remain exploitable in browser-like contexts. The issues are resolved in Firefox 149.0.2 and Thunderbird 149.0.2.

Affected products

Mozilla Firefox < 149.0.2
Mozilla Thunderbird < 149.0.2

Timeline

2026-04-07: disclosed
2026-04-07: patched
2026-04-07: advisory

References

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