VulnerabilityPublished 19 May 2026Updated 20 May 2026

CVE-2026-8961: Mozilla Firefox · CWE-290

Affects Mozilla FirefoxSource CVE Database V5

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

Data as of 29 Oct 2026, 19:04 UTC

CVSS 3.1 base score

6.5Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 25% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available

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

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

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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
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: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 May 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 29 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
Mozilla Firefox	Affected <151	Fixed in 151

AI-suggested

This vulnerability is fixed in Firefox 151 and Firefox ESR 140.11. Users and administrators should update affected Firefox installations to these versions or later to mitigate the risk. Since the vendor advisory confirms the fix, no additional mitigation steps are required beyond applying the official update.

Description

CVE-2026-8961 is a spoofing vulnerability in the Form Autofill component of Mozilla Firefox. This issue could allow an attacker to present deceptive information to users via the autofill feature. The vulnerability has been fixed in Firefox 151 and Firefox ESR 140.11. The CVSS score is 6.5, indicating a medium severity level. No known exploits are reported in the wild. The vendor advisories confirm that the issue is resolved in the specified Firefox versions.

Impact

The vulnerability allows an attacker to spoof information in the Form Autofill component, potentially misleading users and causing them to enter sensitive data into malicious forms. The integrity of autofill data can be compromised, but there is no direct confidentiality or availability impact. No known exploits have been reported in the wild, reducing immediate risk. The medium severity reflects the potential for user deception but limited direct system compromise.

Summary

CVE-2026-8961 is a spoofing vulnerability affecting the Form Autofill component in Mozilla Firefox. Spoofing vulnerabilities typically involve tricking users into believing that malicious content is legitimate by manipulating UI elements or data presentation. This specific vulnerability was addressed and fixed in Firefox 151 and Firefox ESR 140.11. The CVSS v3.1 base score is 6.5, with vector AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N, indicating network attack vector, low attack complexity, no privileges required, user interaction required, unchanged scope, no confidentiality impact, high integrity impact, and no availability impact. The vendor advisories from Mozilla confirm the fix and provide additional context on related vulnerabilities patched in the same releases.

CWE-290Authentication Bypass by Spoofing (opens in a new tab)
Base weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.
OWASP Cheat Sheets
REST Security (opens in a new tab)
JSON Web Token for Java (opens in a new tab)
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V3.5.1 (opens in a new tab)
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
Attack patterns
Creating a Rogue Certification Authority Certificate (opens in a new tab)
Web Services API Signature Forgery Leveraging Hash Function Extension Weakness (opens in a new tab)
Signature Spoof (opens in a new tab)
Signature Spoofing by Misrepresentation (opens in a new tab)
Session Credential Falsification through Prediction (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 May 2026, 20:41 UTC

WeaknessesCWE-290

Technical details

References

Community reviews

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