CVE-2020-6809Public exploitNetwork attack vector

Local file disclosure via same-origin extension fetch

Published Mar 25, 2020 · Updated Aug 4, 2024

Information disclosure in Mozilla Firefox before 74 allows attackers controlling an all-URLs WebExtension to read local files. WebExtensionPolicy::CanAccessURI treats covered file URLs as loadable by the extension principal, so a same-origin Fetch request returns their contents. An attacker must control an installed extension with the all-URLs permission; Mozilla reproduced the behavior on Linux and Windows, but not macOS.

CVSS severity7.5
High
EPSS probability1.48%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Mozilla Firefox before 74 allows attackers controlling an all-URLs WebExtension to read local files. WebExtensionPolicy::CanAccessURI treats covered file URLs as loadable by the extension principal, so a same-origin Fetch request returns their contents. An attacker must control an installed extension with the all-URLs permission; Mozilla reproduced the behavior on Linux and Windows, but not macOS.

The record

CVE
CVE-2020-6809
Published
Mar 25, 2020
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
T1005
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <74

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <74

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

T1005Data from Local System

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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