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CVE-2026-4720— Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149

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等都是美国Mozilla基金会的产品。Mozilla Firefox是一款开源Web浏览器。Mozilla Firefox ESR是Firefox(Web浏览器)的一个延长支持版本。Mozilla Thunderbird是一套从Mozilla Application Suite独立出来的电子邮件客户端软件。 Mozilla多款产品存在安全漏洞，该漏洞源于存在内存安全缺陷，可能导致内存损坏并执行任意代码。以下产品及版本受到影响：Firefox 149之前版本、Firefox E

AI Predicted 8.6 Difficulty: Hard EPSS 0.42% · P34

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 4

VendorProduct Version RangeStatus
Mozilla Firefox 140.9≤ 140.* unaffected
149≤ * unaffected
Mozilla Thunderbird 140.9≤ 140.* unaffected
149≤ * unaffected
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I. Basic Information for CVE-2026-4720

Vulnerability Information
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Vulnerability Title
Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149
Source: CVE Program / CVE List V5
Vulnerability Description
Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
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多款产品 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mozilla Firefox等都是美国Mozilla基金会的产品。Mozilla Firefox是一款开源Web浏览器。Mozilla Firefox ESR是Firefox(Web浏览器)的一个延长支持版本。Mozilla Thunderbird是一套从Mozilla Application Suite独立出来的电子邮件客户端软件。 Mozilla多款产品存在安全漏洞，该漏洞源于存在内存安全缺陷，可能导致内存损坏并执行任意代码。以下产品及版本受到影响：Firefox 149之前版本、Firefox E
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 140.9 ~ 140.* -
Mozilla Thunderbird 140.9 ~ 140.* -

II. Public POCs for CVE-2026-4720

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III. Intelligence Information for CVE-2026-4720

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Vendor Advisories for CVE-2026-4720 (5)

Same Patch Batch · Mozilla · 2026-03-24 · 47 CVEs total

CVE-2026-4714 Incorrect boundary conditions in the Audio/Video component
CVE-2026-4717 Privilege escalation in the Netmonitor component
CVE-2026-4726 Denial-of-service in the XML component
CVE-2026-4719 Incorrect boundary conditions in the Graphics: Text component
CVE-2026-4729 Memory safety bugs fixed in Firefox 149 and Thunderbird 149
CVE-2026-4721 Memory safety bugs fixed in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9,
CVE-2026-3889 Spoofing issue in Thunderbird
CVE-2026-4371 Out of bounds read in IMAP parsing
CVE-2026-4718 Undefined behavior in the WebRTC: Signaling component
CVE-2026-4715 Uninitialized memory in the Graphics: Canvas2D component
CVE-2026-4716 Incorrect boundary conditions, uninitialized memory in the JavaScript Engine component
CVE-2026-4713 Incorrect boundary conditions in the Graphics component
CVE-2026-4725 Sandbox escape due to use-after-free in the Graphics: Canvas2D component
CVE-2026-4712 Information disclosure in the Widget: Cocoa component
CVE-2026-4710 Incorrect boundary conditions in the Audio/Video component
CVE-2026-4711 Use-after-free in the Widget: Cocoa component
CVE-2026-4709 Incorrect boundary conditions in the Audio/Video: GMP component
CVE-2026-4708 Incorrect boundary conditions in the Graphics component
CVE-2026-4707 Incorrect boundary conditions in the Graphics: Canvas2D component
CVE-2026-4706 Incorrect boundary conditions in the Graphics: Canvas2D component

Showing top 20 of 47 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Firefox
Same vendor: Mozilla

V. Comments for CVE-2026-4720

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