What is CVE-2026-6783?

CVE-2026-6783 is a medium-severity vulnerability in Mozilla Firefox, classified under Integer Overflow or Wraparound. CVSS score: 5.3/10. Published 2026-04-21.

How severe is CVE-2026-6783?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Integer overflow in Mozilla Firefox

CVE-2026-6783

Incorrect boundary conditions, integer overflow in the Audio/Video: Playback component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.

Vulnerability class: Integer Overflow

Published 2026-04-21 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.004 (29.4th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 29th percentile — 29.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002

Affected products

Mozilla Firefox — versions 150
Mozilla Thunderbird — versions 150

Weakness classification (CWE)

CWE-190 — Integer Overflow or Wraparound

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-30/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-33/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-6783?: CVE-2026-6783 is a medium-severity vulnerability in Mozilla Firefox, classified under Integer Overflow or Wraparound. CVSS score: 5.3/10. Published 2026-04-21.
How severe is CVE-2026-6783?: Medium severity. CVSS v3 base score is 5.3 out of 10.