Vulnary
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Critical· 9.8official fix available

CVE-2026-8091

A flaw in Mozilla’s audio and video playback component can let an attacker run arbitrary code on a victim’s computer. The bug is caused by incorrect boundary checks that can corrupt memory. It is fixed in newer releases of Firefox and Thunderbird.

publishedMay 7, 2026
last modifiedJul 22, 2026
sourcesNVD
severity · cvss
9.8
critical · how bad it is
exploitation · epss
<1%
38th percentile · chance of exploitation in 30 days
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →
auto-deletes from the system
counting…on Aug 25, 2026

An official fix is available, so this entry is kept for 30 days and then removed automatically.

01

Who is affected

Mozilla Firefox and Thunderbird users running versions older than Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, Thunderbird ESR 140.10.1, or Firefox ESR 115.35.2.

02

Real-world impact

An attacker could execute malicious code on the victim’s machine, potentially stealing personal data, taking control of the system, or installing malware.

03

Why this severity

The CVSS score of 9.8 reflects that the vulnerability can be exploited remotely without authentication, with no user interaction, and it compromises confidentiality, integrity, and availability of the affected system.

04

What to do about it

official fix available
recommended steps
  1. 011. Check the current version of Firefox or Thunderbird.
  2. 022. Download the latest stable release (Firefox 150 or newer, Thunderbird 150 or newer) or the latest ESR release (Firefox ESR 140.10.1 or newer, Thunderbird ESR 140.10.1 or newer, or Firefox ESR 115.35.2 or newer).
  3. 033. Install the update using the installer or the built‑in update mechanism.
  4. 044. Restart the application to complete the update.

NVD-referenced vendor advisory

05

Timeline

  1. May 7, 2026 · May 7, 2026
    Published
    Disclosed and added to the National Vulnerability Database.
  2. Jul 22, 2026 · 14d ago
    Advisory updated
    The NVD record was last revised.
  3. Jul 26, 2026 · 10d ago
    Official fix available
    A vendor patch or mitigation now exists — see the remediation steps above.
06

How it’s attacked

Attack vectorNetwork (remote)
Attack complexityLow
Privileges requiredNone
User interactionNone needed
ScopeUnchanged
Confidentiality impactHigh
Integrity impactHigh
Availability impactHigh
07

References & advisories

NVD advisory ↗Search advisories ↗
(ai-assisted) A model wrote this summary from the official data, so double-check it against the source before you act on it. Read the official advisory →