CVE-2017-5399: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 2.2% chance of exploitation in the next 30 days.

Memory safety bugs were reported in Firefox 51. Some of these bugs showed evidence of memory corruption and we presume that with enough effort that some of these could be exploited to run arbitrary code. This vulnerability affects Firefox < 52 and Thunderbird < 52.

Affected products

• Mozilla Firefox: before 52.0 (fixed in 52.0)
• Mozilla Thunderbird: before 52.0 (fixed in 52.0)

Published 2018-06-11. Last modified 2026-06-17.