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CVE-2026-74986— Site isolation issue in the CSS Parsing and Computation 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 154之前版本和Firefox ESR 153.1之前版本存在安全漏洞，该漏洞源于CSS解析和计算组件中的站点隔离问题，可能导致浏览器安全防护被绕过。

AI Predicted 4.3 Difficulty: Theoretical EPSS 0.35% · P28

Possible ATT&CK Techniques 1 AI

T1200 · Hardware Additions

Affected Version Matrix 4

VendorProduct Version RangeStatus
Mozilla Firefox 153.1≤ 153.* unaffected
154≤ * unaffected
Mozilla Thunderbird 153.1≤ 153.* unaffected
154≤ * unaffected
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I. Basic Information for CVE-2026-74986

Vulnerability Information
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Vulnerability Title
Site isolation issue in the CSS Parsing and Computation component
Source: CVE Program / CVE List V5
Vulnerability Description
Site isolation issue in the CSS Parsing and Computation component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.
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 Firefox 安全漏洞
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 154之前版本和Firefox ESR 153.1之前版本存在安全漏洞，该漏洞源于CSS解析和计算组件中的站点隔离问题，可能导致浏览器安全防护被绕过。
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 153.1 ~ 153.* -
Mozilla Thunderbird 153.1 ~ 153.* -

II. Public POCs for CVE-2026-74986

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III. Intelligence Information for CVE-2026-74986

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Vendor Advisories for CVE-2026-74986 (4)

Same Patch Batch · Mozilla · 2026-08-18 · 58 CVEs total

CVE-2026-74951 Clickjacking issue in Firefox for Android
CVE-2026-74978 Clickjacking issue in the Widget component
CVE-2026-74985 Privilege escalation in the Enterprise Policies component
CVE-2026-74984 Race condition in the JavaScript Engine component
CVE-2026-74979 Mitigation bypass in the Add-ons Manager component
CVE-2026-74982 Denial-of-service in the Widget component
CVE-2026-74958 Information disclosure in the WebRTC component
CVE-2026-74966 Information disclosure in the Form Autofill component
CVE-2026-74956 Same-origin policy bypass in the DOM: Service Workers component
CVE-2026-74952 Privilege escalation in the Application Update component
CVE-2026-74961 Side-channel in the Web Audio component
CVE-2026-74955 Privilege escalation in the Request Handling component
CVE-2026-74954 Information disclosure due to side-channel in the Storage: Cache API component
CVE-2026-74937 Use-after-free in the JavaScript: GC component
CVE-2026-74938 Mitigation bypass in the JavaScript: GC component
CVE-2026-74950 Privilege escalation in the Downloads API component
CVE-2026-74947 Privilege escalation due to invalid pointer in the Graphics component
CVE-2026-74983 Mitigation bypass in the Data Loss Prevention component
CVE-2026-74990 Internally found bugs fixed in Thunderbird ESR 140.14, Thunderbird ESR 153.1 and Thunderbi
CVE-2026-74987 Internally found bugs fixed in Thunderbird ESR 140.14, Thunderbird ESR 153.1 and Thunderbi

Showing top 20 of 58 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Firefox
Same vendor: Mozilla

V. Comments for CVE-2026-74986

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