VulnSocial

CVE-2026-84121Patch(mozilla / firefox)

LOWCVSS 9.6 · CRITICAL

Signal is active with 1 mentions in latest observed window

Immediate actions

  • Patch mozilla firefox systems immediately

Recommended action window: Monitor and triage in normal cycle

NVD description

Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

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0.5/ 10 priority

Sources & remediation

Vendor / third-party advisories
Other references
Weakness type (CWE)
CWE-416

Priority

LOW

Exploitation

NONE

PoC

NONE

Patch

AVAILABLE

Momentum

STABLE

Are you affected?

If you run products in this scope, you should treat this CVE as relevant to your environment.

  • firefox
  • thunderbird

Threat summary

  • Patch or workaround signal is available
  • 2 mentions across 2 observed days
  • Momentum state: stable

What's happening

  • Patch or workaround mentioned in 1 signal
  • Technical details provided in 1 signal
  • General: 1 classified signal
  • Peaked 1d ago at 1 mentions (2026-09-01); latest day: 1
  • 2 total mentions across 2 days

Affected systems

Vendors
mozilla
Products
firefoxthunderbird

Deep dive

Activity timeline2 mentions / 2d
00111Mentions · 2026-09-01: 1Mentions · 2026-09-07: 1Patch / Workaround · 2026-09-01: 1Technical Details · 2026-09-01: 109-0109-07
Signal classification2 categories
Patch
150.0%
General
150.0%
Classification over time
DateTotalLabels
2026-09-011
Patch1
2026-09-071
General1
Full discourse2 posts
  • Upwind Security MDR@UpwindMDR
    Patch

    🚨Critical - Firefox DOM Security Use-After-Free Sandbox Escape (CVE-2026-84121) A use-after-free in Firefox’s DOM security component is remotely reachable via crafted web content; with user interaction it can corrupt memory and escape the sandbox, enabling code execution in the browser context. Fixed in current Firefox and ESR trains. 👉Affected: Mozilla Firefox < 155; Firefox ESR < 115.40 / 140.15 / 153.2 | Upgrade to 155 / 115.40 / 140.15 / 153.2

    Post summary

    Firefox suffers a critical use‑after‑free vulnerability in its DOM security component affecting versions below 155 and certain ESR trains; the issue is fixed in current releases, but no PoC, exploit code, or active exploitation evidence is provided.

    10010133
    296 followersView on X
  • Yaqoub@yyrrw
    General

    CVE-2026-84119 CVE-2026-84121

    Post summary

    The text merely lists two CVE identifiers without any accompanying details or context.

    0000028
    31 followersView on X
CPE platform detail2 entries

2 of 2 entries

PartVendorProductVersionTarget SWTarget HW
Appmozillafirefox---
Appmozillathunderbird---

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