CVE-2026-4687
Published: 24 March 2026
Summary
CVE-2026-4687 is a high-severity Improper Check for Unusual or Exceptional Conditions (CWE-754) vulnerability in Mozilla Firefox. Its CVSS base score is 8.6 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 41.4th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SI-10 (Information Input Validation).
Deeper analysis
CVE-2026-4687 is a sandbox escape vulnerability caused by incorrect boundary conditions in the Telemetry component of Mozilla Firefox and Thunderbird. Published on 2026-03-24, it carries a CVSS v3.1 base score of 8.6 (AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H) and maps to CWE-754 (Improper Check for Unusual or Exceptional Conditions) and CWE-120 (Buffer Copy without Checking Size of Input). The flaw affects Firefox and Thunderbird versions prior to the patched releases.
Remote attackers can exploit this vulnerability over the network with low attack complexity, requiring no privileges, user interaction, or authentication. Exploitation results in a change of scope from the sandboxed context, enabling high-impact availability disruption such as application crashes or denial of service, while confidentiality and integrity remain unaffected.
Mozilla fixed the vulnerability in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. Security advisories MFSA2026-20, MFSA2026-21, MFSA2026-22, and MFSA2026-23, along with Bugzilla entry 2016368, provide further details on the patches and recommend immediate updates to mitigate the risk.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-14798
Vulnerability details
Sandbox escape due to incorrect boundary conditions in the Telemetry component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Sandbox escape with scope change directly enables privilege escalation (T1068) and client-side exploitation (T1203); explicit availability impact via crashes maps to application exploitation for DoS (T1499.004).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely patching and remediation of known flaws like the sandbox escape in CVE-2026-4687 fixed in specified Firefox and Thunderbird versions.
Mandates validation of information inputs to address the buffer copy without size checking (CWE-120) and improper boundary conditions in the Telemetry component.
Implements memory protections to mitigate exploitation of buffer-related vulnerabilities that enable sandbox escapes and availability disruptions.
Hardening callouts derived
Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).
Oracle Linux 8 (3 rules)
- V-248574 YUM must be configured to prevent the installation of patches, service packs, device drivers, or OL 8 system components that have not been digitally signed using a certificate that is recognized and approved by the organization. via CWE-754
- V-248573 The OL 8 file integrity tool must notify the system administrator (SA) when changes to the baseline configuration or anomalies in the operation of any security functions are discovered within an organizationally defined frequency. via CWE-754
- V-248575 OL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. via CWE-754
Oracle Linux 9 (1 rule)
- V-271452 OL 9 must use a Linux Security Module configured to enforce limits on system services. via CWE-754