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CVE-2020-26958

MEDIUM
6.1
CVSS Score
Published: December 9, 2020 at 12:22 AM UTC
Updated: June 17, 2026 at 03:08 AM UTC
3 products affected across 1 vendorFirefoxThunderbirdFirefox ESR

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Severity
MEDIUM6.1
Exploit prediction
EPSS 1%

Description

Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached through a ServiceWorker. This could lead to a cross-site script inclusion vulnerability, or a Content Security Policy bypass. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Firefox· Mozilla
95%
v < 83
Affected range stops below 83, so it looks safe — our inference, not a vendor statement
Affected range stops below 83.0, so it looks safe — our inference, not a vendor statement
Firefox ESR· Mozilla
95%
v < 78.5
Affected range stops below 78.5, so it looks safe — our inference, not a vendor statement
Thunderbird· Mozilla
95%
v < 78.5
Affected range stops below 78.5, so it looks safe — our inference, not a vendor statement

References (4)

x_refsource_MISCIssue TrackingPermissions RequiredVendor Advisory
Source: [email protected]
https://bugzilla.mozilla.org/show_bug.cgi?id=1669355
x_refsource_CONFIRMVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2020-50/
x_refsource_CONFIRMVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2020-51/
x_refsource_CONFIRMVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2020-52/

CVSS

6.1MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-79

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