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CVE-2026-5734— Memory safety bugs fixed in Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2

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多款产品存在缓冲区错误漏洞，该漏洞源于内存安全问题，可能导致内存损坏和执行任意代码。以下产品和版本受到影响：Firefox ESR 140.9.1之前版本、

AI Predicted 8.8 Difficulty: Moderate EPSS 0.33% · P25

Affected Version Matrix 4

VendorProduct Version RangeStatus
Mozilla Firefox 140.9.1≤ 140.* unaffected
149.0.2≤ * unaffected
Mozilla Thunderbird 140.9.1≤ 140.* unaffected
149.0.2≤ * unaffected
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I. Basic Information for CVE-2026-5734

Vulnerability Information
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Vulnerability Title
Memory safety bugs fixed in Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2
Source: CVE Program / CVE List V5
Vulnerability Description
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
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 缓冲区错误漏洞
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多款产品存在缓冲区错误漏洞，该漏洞源于内存安全问题，可能导致内存损坏和执行任意代码。以下产品和版本受到影响：Firefox ESR 140.9.1之前版本、
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 140.9.1 ~ 140.* -
Mozilla Thunderbird 140.9.1 ~ 140.* -

II. Public POCs for CVE-2026-5734

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III. Intelligence Information for CVE-2026-5734

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Vendor Advisories for CVE-2026-5734 (2)

Same Patch Batch · Mozilla · 2026-04-07 · 5 CVEs total

CVE-2026-5731 Memory safety bugs fixed in Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird ESR 140
CVE-2026-5732 Incorrect boundary conditions, integer overflow in the Graphics: Text component
CVE-2026-5733 Incorrect boundary conditions in the Graphics: WebGPU component
CVE-2026-5735 Memory safety bugs fixed in Firefox 149.0.2 and Thunderbird 149.0.2

IV. Related Vulnerabilities

Same product: Firefox
Same vendor: Mozilla

V. Comments for CVE-2026-5734

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