CVE-2020-26978Public exploitNetwork attack vector

Internal host and service probing via unrestricted ports

Published Jan 7, 2021 · Updated Aug 4, 2024

Network probing in Firefox before 84, Firefox ESR before 78.6, and Thunderbird before 78.6 allows remote attackers to probe internal hosts and services. The networking core permitted web requests to H.323, PPTP, and RTSP ports 1720, 1723, and 554 instead of treating them as restricted ports. A user must load malicious web content in a browser-like context; Thunderbird mail reading disables scripting, while reachable local or intranet services determine exposure.

CVSS severity6.1
Medium
EPSS probability1.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Network probing in Firefox before 84, Firefox ESR before 78.6, and Thunderbird before 78.6 allows remote attackers to probe internal hosts and services. The networking core permitted web requests to H.323, PPTP, and RTSP ports 1720, 1723, and 554 instead of treating them as restricted ports. A user must load malicious web content in a browser-like context; Thunderbird mail reading disables scripting, while reachable local or intranet services determine exposure.

The record

CVE
CVE-2020-26978
Published
Jan 7, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
T1046
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

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

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/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

T1046Network Service Discovery

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo