What is CVE-2025-10859?

CVE-2025-10859 is a medium-severity vulnerability in Mozilla Firefox, classified under Exposure of Private Personal Information to an Unauthorized Actor. CVSS score: 4.0/10. Published 2025-09-30.

How severe is CVE-2025-10859?

Medium severity. CVSS v3 base score is 4.0 out of 10.

Is CVE-2025-10859 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Mozilla Firefox

CVE-2025-10859

Cookie storage for non-HTML temporary documents was being shared incorrectly with normal browsing content, allowing information from private tabs to escape Incognito mode even after the user closed all tabs. This vulnerability was fixed in Firefox for iOS 143.1.

EPSS: 0.001 (1.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.0 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.

Affected products

Mozilla Firefox
Mozilla Firefox For Ios — versions 143.1

Weakness classification (CWE)

CWE-359 — Exposure of Private Personal Information to an Unauthorized Actor

Public proof-of-concept exploits

ARPSyndicate/cve-scores

References

security@mozilla.org (Permissions Required, Issue Tracking)
security@mozilla.org (Vendor Advisory)

Frequently asked questions

What is CVE-2025-10859?: CVE-2025-10859 is a medium-severity vulnerability in Mozilla Firefox, classified under Exposure of Private Personal Information to an Unauthorized Actor. CVSS score: 4.0/10. Published 2025-09-30.
How severe is CVE-2025-10859?: Medium severity. CVSS v3 base score is 4.0 out of 10.
Is CVE-2025-10859 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.