CVE-2020-35111Network attack vector

IP address disclosure via missed view-source requests

Published Jan 7, 2021 · Updated Aug 4, 2024

Information disclosure in Mozilla Firefox before 84, Firefox ESR before 78.6, and Thunderbird before 78.6 allows attackers to learn an IP address. The WebExtensions request-handling path fails to invoke an extension's proxy.onRequest callback for view-source URLs covered by its all-URLs filter. Exposure requires such a proxy-enabled extension and a user to open View Source; ordinary web content cannot navigate to the affected URL scheme.

CVSS severity4.3
Medium
EPSS probability1.42%
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 84, Firefox ESR before 78.6, and Thunderbird before 78.6 allows attackers to learn an IP address. The WebExtensions request-handling path fails to invoke an extension's proxy.onRequest callback for view-source URLs covered by its all-URLs filter. Exposure requires such a proxy-enabled extension and a user to open View Source; ordinary web content cannot navigate to the affected URL scheme.

The record

CVE
CVE-2020-35111
Published
Jan 7, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 7, 2021CVE 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 <84

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <84
Mozilla · Thunderbirdversion=unspecified <78.6
Mozilla · Firefox ESRversion=unspecified <78.6

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
4.3NIST NVDAV:N/AC:M/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 exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

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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