CVE-2026-84121— Sandbox escape due to use-after-free in the DOM: Security component
Quick assessment
Affected
Mozilla Firefox
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Mozilla Firefox是Mozilla基金会开源的一款网页浏览器。 Mozilla Firefox 155之前版本、Mozilla Firefox ESR 115.40之前版本、Mozilla Firefox ESR 140.15之前版本、Mozilla Firefox ESR 153.2之前版本、Mozilla Thunderbird 155之前版本、Mozilla Thunderbird 140.15之前版本和Mozilla Thunderbird 153.2之前版本存在资源管理错误漏洞，该漏
Possible ATT&CK Techniques 1 AI
T1059 · Command and Scripting InterpreterAffected Version Matrix 7
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mozilla | Firefox | 115.40≤ 115.* |
unaffected |
140.15≤ 140.* |
unaffected | ||
153.2≤ 153.* |
unaffected | ||
155≤ * |
unaffected | ||
| Mozilla | Thunderbird | 140.15≤ 140.* |
unaffected |
153.2≤ 153.* |
unaffected | ||
155≤ * |
unaffected |
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I. Basic Information for CVE-2026-84121
Vulnerability Information
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Vulnerability Title
Sandbox escape due to use-after-free in the DOM: Security component
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Mozilla Firefox 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mozilla Firefox是Mozilla基金会开源的一款网页浏览器。 Mozilla Firefox 155之前版本、Mozilla Firefox ESR 115.40之前版本、Mozilla Firefox ESR 140.15之前版本、Mozilla Firefox ESR 153.2之前版本、Mozilla Thunderbird 155之前版本、Mozilla Thunderbird 140.15之前版本和Mozilla Thunderbird 153.2之前版本存在资源管理错误漏洞，该漏
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| Mozilla | Firefox | 115.40 ~ 115.* | - |
|
| Mozilla | Thunderbird | 140.15 ~ 140.* | - |
|
II. Public POCs for CVE-2026-84121
| # | POC Description | Source Link | Shenlong Link |
|---|
AI-Generated POC
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Vendor Advisories for CVE-2026-84121 (7)
Same Patch Batch · Mozilla · 2026-09-01 · 34 CVEs total
| CVE-2026-84123 | Privilege escalation due to use-after-free in the Graphics: WebGPU component | |
| CVE-2026-84132 | Information disclosure in the Networking: HTTP component | |
| CVE-2026-84130 | Information disclosure in the Graphics: WebGPU component | |
| CVE-2026-84129 | Site isolation issue in the DOM: Navigation component | |
| CVE-2026-84128 | Privilege escalation in the WebDriver BiDi component | |
| CVE-2026-84127 | Information disclosure in the WebExtensions component in Firefox for Android | |
| CVE-2026-84126 | Incorrect boundary conditions in the Layout: Grid component | |
| CVE-2026-84125 | Use-after-free in the DOM: Core & HTML component | |
| CVE-2026-84124 | Use-after-free in the DOM: Core & HTML component | |
| CVE-2026-84133 | Site isolation issue in the DOM: Push Subscriptions component | |
| CVE-2026-84122 | Use-after-free in the Audio/Video component | |
| CVE-2026-84118 | Use-after-free in the JavaScript: GC component | |
| CVE-2026-84117 | Privilege escalation in Firefox for Android | |
| CVE-2026-84145 | Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR | |
| CVE-2026-84131 | Privilege escalation due to invalid pointer in the Graphics component | |
| CVE-2026-84120 | Use-after-free in the Audio/Video component | |
| CVE-2026-84119 | Sandbox escape due to use-after-free in the DOM: Navigation component | |
| CVE-2026-84642 | Allowed UNC hostnames for attachments interpreted as a regular expression | |
| CVE-2026-84134 | Other issue in the Profile Backup component | |
| CVE-2026-84135 | Other issue in Firefox Focus for Android |
Showing top 20 of 34 CVEs. View all on vendor page → →
IV. Related Vulnerabilities
Same product: Firefox
-
CVE-2026-84144
Internally found bugs fixed in Thunderbird 155 and Thunderbi -
CVE-2026-84143
Internally found bugs fixed in Thunderbird 155, Thunderbird -
CVE-2026-84142
Internally found bugs fixed in Thunderbird 155 -
CVE-2026-84141
Integer overflow in the Graphics: ImageLib component -
CVE-2026-84140
Site isolation issue in the DOM: Navigation component
Same vendor: Mozilla
-
CVE-2026-86853
Repeated external URL scheme launches could potentially caus -
CVE-2026-84642
Allowed UNC hostnames for attachments interpreted as a regul -
CVE-2026-84640
One byte overflow read in mail parser -
CVE-2026-84641
Information disclosure due to malicious IMAP server response -
CVE-2026-84639
Uninitialized memory in MIME parsing
V. Comments for CVE-2026-84121
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