Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-84138

CVE-2026-84138MEDIUM

Mozilla Firefox — Denial-of-service in the PDF Viewer component

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   R  U  N  N  H    6.5   .0037   28.9     —

AFFECTED
  Product      Versions     Fixed
  Firefox      unspecified  155
  Thunderbird  unspecified  155

TIMELINE
  Sep 1   Reserved by mozilla
  Sep 1   Published (CNA: mozilla)
  Sep 3   RESCORED — CVE-2026-84138 (Mozilla Firefox). CVSS 7.5 → 6.5 (NVD).

CWE-400 · CNA: mozilla · CVSS v3.1 · 3 references · NVD status: Modified

Description

Denial-of-service in the PDF Viewer component. This vulnerability was fixed in Firefox 155 and Thunderbird 155.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
September 1, 2026	Reserved	Reserved by mozilla
September 1, 2026	Published	Published (CNA: mozilla)
September 3, 2026	RESCORED	RESCORED — CVE-2026-84138 (Mozilla Firefox). CVSS 7.5 → 6.5 (NVD).

Affected

Affected products and packages — 2 rows
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
Mozilla	Firefox	—	—	155
Mozilla	Thunderbird	—	—	155

Weaknesses

CWE-400

References (3)

https://bugzilla.mozilla.org/show_bug.cgi?id=2056164 [Issue Tracking]
https://www.mozilla.org/security/advisories/mfsa2026-82/ [Vendor Advisory]
https://www.mozilla.org/security/advisories/mfsa2026-86/ [Vendor Advisory]

Authoritative record: CVE-2026-84138 at cve.org

Vendors: mozilla

Weaknesses: CWE-400

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-84138 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.