CVE-2020-26978

Name: CVE-2020-26978
Creator: NVD / NIST
Published: 2021-01-07T14:15:12.297+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.1/10EPSS 1.28%

Last modified Jun 17, 2026

CVE-2020-26978 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. Using techniques that built on the slipstream research, a malicious webpage could have exposed both an internal network's hosts as well as services running on the user's local machine. This vulnerability affects Firefox < 84, Thunderbird < 78.6, and Firefox ESR < 78.6.. EPSS estimates a 1.28% chance of exploitation in the next 30 days.

Description

Using techniques that built on the slipstream research, a malicious webpage could have exposed both an internal network's hosts as well as services running on the user's local machine. This vulnerability affects Firefox < 84, Thunderbird < 78.6, and Firefox ESR < 78.6.

Metrics

CVSS 3.1

6.1/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS Probability

1.28%

66.3th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 84.0
Mozilla	Firefox Esr	< 78.6.0
Mozilla	Thunderbird	< 78.6.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1677047Permissions Required
https://www.mozilla.org/security/advisories/mfsa2020-54/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-55/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-56/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1677047Permissions Required
https://www.mozilla.org/security/advisories/mfsa2020-54/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-55/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-56/Vendor Advisory

Timeline

Published: Jan 7, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-26978?

How severe is CVE-2020-26978?

CVE-2020-26978 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 1.28% probability of exploitation in the next 30 days.

How do I fix CVE-2020-26978?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2020-26978?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST