Mozjs52: [Unknown description] (CVE-2026-84134)

CVE-2026-84134 is a security vulnerability identified in the mozjs52 JavaScript engine component used in various Ubuntu LTS releases. The vulnerability is referenced in the Mozilla Foundation Security Advisory 2026-82 as an 'other issue' in the Profile Backup component with low impact. Although the CVSS score is high (9.8), the advisory classifies the impact as low for this specific CVE. The vulnerability was present in multiple specific package versions of mozjs52 across Ubuntu 18.04, 20.04, 22.04, and 24.04 LTS. The issue was fixed in Firefox 155, as stated in the vendor advisory. No exploitation in the wild has been reported. The advisory groups this CVE among several other security fixes in Firefox 155, addressing various memory corruption and security defects.

The vulnerability has a high CVSS base score of 9.8, indicating potential for severe impact including confidentiality, integrity, and availability loss. However, the Mozilla advisory categorizes the impact of CVE-2026-84134 specifically as low, describing it as an 'other issue' in the Profile Backup component. There are no known active exploits in the wild. The vulnerability affects multiple Ubuntu LTS versions through specific mozjs52 package versions. Successful exploitation could potentially affect the security of the Firefox browser environment until patched.

An official fix for CVE-2026-84134 is available and was released in Firefox 155. Users and administrators should upgrade affected mozjs52 packages to versions that include the Firefox 155 fixes or later. Since this is not a cloud service, manual patching or upgrading is required. No additional mitigation steps are indicated by the vendor advisory.