Report · SecurityWeekAbout CVE-2026-6770Published 27 Apr 2026

Firefox Vulnerability Allows Tor User Fingerprinting

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Authoritative record:CVE-2026-6770· Medium 6.5

Not known to be exploited · CVSS 6.5 Medium · patch available : update Firefox when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Firefox	Affected <150	Fixed in 150

AI-suggested

This vulnerability has been officially patched by Mozilla and the Tor Project. Users should update to Firefox 150 or later and Tor Browser 15.0.10 or later to mitigate this issue. No additional user action is required beyond applying these updates. Patch status is confirmed by vendor advisories.

Description

The vulnerability is tracked as CVE-2026-6770 and it has been patched with the release of Firefox 150 and Tor 15.0.10. The post Firefox Vulnerability Allows Tor User Fingerprinting appeared first on SecurityWeek .

Impact

The vulnerability allows threat actors to fingerprint users in Firefox's Private Browsing mode and Tor Browser's New Identity sessions by linking activity across different sites without relying on cookies or shared storage. This undermines privacy protections intended to isolate browsing sessions and protect user anonymity. The fingerprint persists until the browser process is restarted. There are no known exploits in the wild reported at this time.

Summary

The vulnerability CVE-2026-6770 affects Firefox and the Tor Browser by leaking a stable identifier via the IndexedDB API. Firefox stores IndexedDB database names with internal UUID mappings, and the order in which these databases are listed remains consistent across different sites during the same browser session. This consistency allows unrelated websites to link user sessions and fingerprint users despite Private Browsing mode or Tor's New Identity feature, which are designed to isolate user activity. Mozilla rated the issue as medium severity and patched it in Firefox 150. The Tor Project also incorporated the fix in Tor Browser 15.0.10.

References

securityweek.com/firefox-vulnerability-allows-tor-user-fingerprinting/ (opens in a new tab)

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